The true Catholic Church is wherever the four marks are kept intact. That is NOT Vatican II or anything related to it.
The true Catholic Church is wherever the First Commandment is still obeyed as God intended it to be. That is NOT Vatican II or anything related to it.
The true Catholic Church is wherever there are no recessions from any point of doctrine proposed by her authoritative Magisterium. That is NOT Vatican II or anything related to it.
The Catholic Church is NOT wherever there is "visibility" because Budhism, Judaism and Islam are just as visible or more so than the Novus Ordo, Vatican II, SSPX, CMRI and other such false sects. That makes them no more or less valid.
The Arian 'church' was much more visible than the Cathoic Church, but was obviously not the true Catholic Church.
As for when the true Catholic Church was "lost": Never. That is impossible. It cannot ever be lost, only individual members who turn away from God can be lost.
While I was with them, I kept them in thy name. Those whom thou gavest me have I kept; and none of them is lost, but the son of perdition, that the scripture may be fulfilled.