In my opinion, the excerpt above from the CE article on Galileo properly explains how the Church’s magisterium is not to be accused of the errors Cassini attributes to it (and consequently, there is no wound to indefectibility, or any need to declare sede vacante from 1616).

Magisterium??? What magisterium?

The closest thing to infallibility on the matter is the condemnation of Galileo and it isn't even magisterial.

He's conflating about 3 different issues to continue promoting his Old Catholic ecclesiology.

Reality.  You conflated the question of whether a decree of the Holy Office is Magisterial and irreformable (there's disagrement on that), and then slide that over into the issue of indefectibility (which entails begging the question, even against your opinion regarding the first) and then claiming the SV principles would require SV from 1616.  It's an idiotic conflation of 3 separate issues in an attempt to smear SVs with a false argument ad absurdum that they would hold the See to be vacant since 1616.  Idiotic on all counts.  Not sure if the conflation was the result of your childish petulance regarding or befuddlement of your foggy mind.

Correct, which is where you should have stopped.  You're the one that started babbling on about indefectibility and a vacant see since 1616.

Sean,

In other words, the condemnations of Galileo were not universal teachings issued to the Church on the question of whether heliocentrism was heresy, but were limited to the issue at hand - condemning Galileo's writings and proscribing them, and him, from opining as written. The assertions of heliocentrism as heresy were tangential to the precise issue and holding, and not an expression of the ordinary, universal magisterium.

Therefore, the Church could change its stance on heliocentrism and allowing its written expressions - that would merely be at the level of a practical, disciplinary change under different historical circuмstances.

Is that a decent summary?

I don't find that particularly comforting - i.e., that the Holy Office, with the pope's approval, could be so "wrong" about what is heresy and contrary to the teaching of the Fathers. The authority of the Church as teacher on issues of faith is still eroded and damaged.

It would seem to me that such a situation implicates - again and again we come back to this - the Church's indefectibility, which, as far as accepted wisdom or expression goes, is not limited to the infallible.

If necessary, I can go get that Canon Smith article about when the Church is indefectible - I believe it would cover things like the Holy Office condemnation of Galileo.

So we are not talking only about ex cathedra, at least under the accepted or conventional understanding.

DR