I know the difference.
It doesn't appear that you do.
If a couple are actually married,
no one, save God or death, can dissolve it, not even the Pope (thus why I recommended looking at Henry VIII).
A finding of nullity by the Church is a declaration that there was something, at the time of the exchange of vows, that impeded the ability of one or both of the parties to enter into the marriage contract.
Something that needs to also be said is that the declaration of nullity is NOT infallible. The legitimate purpose for examining a marriage is so that people of good will can have MORAL certitude about their marital status. If they are not of good will and are just "playing the system" to get their declaration, no "power to loose" is going to save them (excepting, of course, they make a valid confession and are absolved). Now a declaration of nullity (DoN) is
binding, that is clergy are bound to accept the finding, even if they themselves have doubts about it. Obviously, in the present situation, not many trust
anything that comes out of Rome or the diocesan tribunals, which is why trad clergy often do not feel bound by a DoN, and want to examine the case themselves.