I was alive and paying attention during Vatican II, and the historical record bears this out: the final docuмent to be rammed through was
Dignitatis humanae, the English title being the Declaration on Religious Freedom.
It was as a matter of fact, the FIRST docuмent the progressive hijackers of the Council attempted to bring up for a vote at the start in 1962. It met with such outspoken opposition that they shelved it and then kept trying to sneak it in over the subsequent 3 years, until at last, they were reduced to some creepy tricks to push it through at the last minute, seemingly when the remaining attendees were anxious to go home so they passed the thing just to get it over with. The rest is history.
Never before in the history of the Church has such liberalism been countenanced by Catholic bishops or a reigning Pope. In fact, there have been particular condemnations against such bad doctrine by good popes such as Bl. Pius IX in his Syllabus of Errors. Pope Leo XIII and St. Pius X warned the faithful of the world about the movement to make religious freedom newly acceptable.
There are other glaring departures from Sacred Tradition in Vat.II, but the above stands out as the most subversive.
For example, the Church has always been identified as being one and the same as the Church of Christ, but in A.D. 1963 a docuмent
(Lumen gentium) was prepared which subtly snuck in the word
"subsistit" (Latin for
subsists in, but has a more pernicious theological connotation in the Latin). In
LG 8, it says, "The Catholic Church ... subsists in the Church of Christ."
That is a half truth, and a half truth is a whole lie, therefore it is a heresy -- if not literally in itself, then as it was interpreted and preached even to this day (A.D. 2016). This was later revealed to have been the brainchild of a Protestant observer who recommended inserting
"subsistit" to a Catholic peritus who then suggested it to his bishop, who then recommended it to the progressivist usurpers, who then inserted it into the docuмent. Consequently, there were priests who took this heretical novelty into the parishes of the world and concluded to the Catholics who listened to them that "As of this publication, we now know that there is indeed salvation outside the Church." Notice that Vatican II did not pronounce that
EENS (extra ecclesiam nulla salus) has been abrogated (because a dogmatically defined doctrine cannot be abrogated, now or ever) but that is exactly what the liberals SAID had happened, and there was no one to correct them or to expose them officially of their error. Such luminaries as Fr. Feeney warned Catholics for the previous 20+ years that this was a danger and was growing in popularity in the highest offices of the Church but there was not a word of correction or re-pronouncement of the thrice-defined
EENS.
There are more examples.
ETA: I am not a sedevacantist.