Whether or not a Council decides to issue a solemn definition, the understanding of the Church has always been that when a moral universality of the bishops (i.e. nearly all of them) get together and teach in union with the Pope, that the teaching is protected from any substantial grave error by the Holy Spirit.

^^^ False NO new doctrine. This is one of the diabolical new doctrines of V2, taught only in Lumen Gentium (#25.2) and is strictly the understanding of the V2 church, not the Catholic Church. This aberation of Pentecost is not to be found anywhere in Church teachings.  

25.2 Although the individual bishops do not enjoy the prerogative of infallibility, they nevertheless proclaim Christ's doctrine infallibly whenever, even though dispersed through the world, but still maintaining the bond of communion among themselves and with the successor of Peter, and authentically teaching matters of faith and morals, they are in agreement on one position as definitively to be held. This is even more clearly verified when, gathered together in an ecuмenical council, they are teachers and judges of faith and morals for the universal Church, whose definitions must be adhered to with the submission of faith. - Pope Paul VI, Lumen Gentium

^^^ False NO new doctrine. This is one of the diabolical new doctrines of V2, taught only in Lumen Gentium (#25.2) and is strictly the understanding of the V2 church, not the Catholic Church. This aberation of Pentecost is not to be found anywhere in Church teachings.  

25.2 Although the individual bishops do not enjoy the prerogative of infallibility, they nevertheless proclaim Christ's doctrine infallibly whenever, even though dispersed through the world, but still maintaining the bond of communion among themselves and with the successor of Peter, and authentically teaching matters of faith and morals, they are in agreement on one position as definitively to be held. This is even more clearly verified when, gathered together in an ecuмenical council, they are teachers and judges of faith and morals for the universal Church, whose definitions must be adhered to with the submission of faith. - Pope Paul VI, Lumen Gentium

Ridiculous.  You cite Lumen Gentium as your authority, from a Council that you reject as heterodox and/or heretical.

Besides that, you need to do some work on your reading comprehension.  This is merely saying that their solemn definitions must be accepted de fide and does not address the question of whether or not the Council can teach heresy and wreck the Church.  I've cited a PRE-Vatican II source which says that it cannot due to the overall guidance of the Church by the Holy Spirit due to the promises of Our Lord.

Your position is heretical, Stubborn, without any question.  You consider the Magisterium to be defectible.

does not address the question of whether or not the Council can teach heresy and wreck the Church.  I've cited a PRE-Vatican II source which says that it cannot due to the overall guidance of the Church by the Holy Spirit due to the promises of Our Lord.

But what does "teach" mean in the context of a council?  Or when we say the magisterium has "taught", does that not imply binding, unchanging facts (i.e. doctrine)?  What's the point of "teaching" something that isn't required to be believed?
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Example:  You go to math class and learn "math doctrine" (facts and truths which must be believed, else you can't do math):  2+2=4, 10x10=100, etc.
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You're saying that one can go to math class and learn non-fact/theory (does the number "Pi" go to infinity?  How many prime numbers are there?) and that such theory/opinion can't be wrong?  Yet, such theories/opinions aren't required to be learned to do math.  If they can't be wrong, why aren't they required?
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In the context of Catholicism, you're arguing that the non-infallible magisterium can "teach" (to use the term loosely) but such "teachings" aren't required to be believed, even though they can't be wrong?  It makes no sense.  Seems like a whole waste of time.  Can you provide an example of any such "teaching" prior to V2?
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The way I see it is the non-infallible Magisterium is supposed to re-iterate, re-teach and clarify the doctrines that have existed from Tradition/Scripture/Christ.  All doctrine was given to the Church in Christ's time, either explicitly or implicitly.  So the Magisterium's job is to "hand down that which has always been taught" and to clarify and re-teach when heresies and misunderstandings arise.  It does these jobs using either 1) solemn infallible statements (unusual), 2) non-solemn infallible statements (papal clarification that doctrine x is of Tradition/Scripture), or 3) through the ordinary teaching offices of orthodox bishops/priests/theologians who re-teach Truths which are the same "yesterday, today and tomorrow".
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The Magisterium is composed of past apostles/saints/popes/clergy and also current pope/clergy.  Scripture/Tradition/History are the tools used, but since the Magisterium is an "office", so only men can fulfill its duties.  So, for example, St Alphonsus' writings or St Thomas' Summa is (generally) part of the magisterium because they have been proven to be orthodox by their peers and by saintly clergy and approved by popes.  But not everything coming from a pope/saint is correct, so God gave us Church history to double-check orthodoxy.  God also gave us the Church Fathers who in many areas, all agree on doctrine, which they received from the Apostles, so we can be confident that our Tradition is orthodox. 
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When a pope is not acting in his official capacity as Authoritative Teacher 1) solemnly or 2) non-solemnly but still authoritatively, then he is 3) just a simple bishop giving us his theological opinion.  Same applies to all bishops/priests in the world.  If any cleric (including the pope) is not basing their "teachings" on orthodoxy from 1) prior doctrinal councils, 2) Tradition/Church Fathers, 3) non-conciliar dogmatic statements, or 4) confirmed Scriptural truths, then how can it be truly Catholic?  Where is this "teaching" coming from, that we must believe it?  What foundation is it based on? 
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There is nothing new under the sun.  All Church doctrine has been revealed to us.  The Assumption dogma was not new by any means.  And the yet-to-be-defined truth of "Our Lady, Mediatrix of All Graces" is still implicitly part of the Faith, even though the Church has not defined it as such.  V2 didn't re-teach, clarify, or re-affirm orthodoxy, so its conclusions are novel and uncatholic.  This does not jeopardize the Magisterium's function or sublime nature at all, for the Magisterium (i.e. the men of today) are not protected from error, just like 98% of such fell into error during Arianism.  What is protected by the Holy Ghost, until the end of time, is the ETERNAL MAGISTERIUM, which is all orthodox/Divine Teachings of Scripture/Tradition/Doctrine that Christ gave to His Apostles and which their successors have guarded for 2,000 years.

That's not what I'm saying at all.  They didn't know who the real pope was and to whom they had to owe obedience and whose Magisterium they would have to submit to if it were to teach.

You do realize that material error does not exclude from membership in the Church, right?

That's another reason, BTW, that R&R is much more pernicious and potentially harmful to the faith than sedevacantism.  Sedevacantists at least formally acknowledge that they have a duty to submit to Church Magisterium, whereas the R&R dispute this.  So, if they're wrong, the sedevacantists are in material error, but the R&R are in danger of formal error due to their attitudes toward Church authority.

You wrote, "in one sense it was a question of attempting to discern where the Church was"
This is wrong. Nobody of note at that time wondered "where" the Church was. Just as they don't wonder where it is when a pope dies.

You wrote, "in one sense it was a question of attempting to discern where the Church was"
This is wrong. Nobody of note at that time wondered "where" the Church was. Just as they don't wonder where it is when a pope dies.

No, not really. You had sides of the Great Western Schism practically declare holy war on each other, and countless common Catholics even moved city so they could be under who they viewed as the true pope. Among the monarchs, they all picked which pope to follow, and since the popes didn't recognise each other at all, their Churches were clearly separate entities, however similar they may have been. 

Yes, really. What history book have you seen it written in that they considered a false claimant and his followers to be another Church?

The papal claimants all excommunicated each other. Those who are excommunicated are outside of the Church. Therefore, when one picked a pope to follow, one had to decide where the Church was, since only one claimant was the true leader of the Church and the rest weren't even in it at all. It logically follows that they were making a judgement on where the Church was, whether they were explicitly saying that or not.

The raising of the Oriflamme etc. as I brought up also indicates that people saw followers of the other claimants as outside of the Church.

Giving it a bit of thought, if +Schneider and +Vigano are in good standing with the Church while holding that there are errors in Vatican II, then what is the obstacle for SSPX joining back in full communion with Rome?

Part of the obstacle beforehand had been that the SSPX had to accept all of Vatican II, at least by applying a hermeneutic of continuity.  Here we have two bishops in good standing agreeing with them that there are in fact errors in Vatican II (they probably have the same errors in mind that the SSPX does).

So either +Schneider and +Vigano need to get the boot, or else the SSPX needs to be let back in while being allowed to hold that there are errors in V2.

The papal claimants all excommunicated each other. Those who are excommunicated are outside of the Church. Therefore, when one picked a pope to follow, one had to decide where the Church was, since only one claimant was the true leader of the Church and the rest weren't even in it at all. It logically follows that they were making a judgement on where the Church was, whether they were explicitly saying that or not.

The raising of the Oriflamme etc. as I brought up also indicates that people saw followers of the other claimants as outside of the Church.

It's been a long time since the so-called Western Schism. No books have stated any such thing, which shows you are doing your own reasoning and claiming an historical fact that simply was not.