At the end of the day, you reduce the Magisterium to nothing more than a man (the Pope) or a group of men (Fathers of Vatican II) opining about doctrinal matters. If what they happen to say is true, then it has authority. If what they happen to say is false (by my judgment), then it has no authority.
If they do not engage the solemn magisterium and teach 'with certainty of faith' then their magisterium is FALLIBLE and CONDITIONAL, ergo, yes - they are teaching with their simple authority inherent in their offices as simple bishops, or theologians.
And yes, in this case, the litmus test is whether or not their fallible teachings AGREE WITH TRADITION and the UNIVERSAL MAGISTERIUM (which is the CONSTANT teachings over the 2,000 years of the church, not (as you incorrectly define it) as being "universal" just because it came from an ecuмenical council.) The word "universal" means over the course of Church history. It refers to the past magisteriums of the Church; it does not refer to the PRESENT DAY in any scenario. If you would change your mindset on this, you might figure things out.