Quite often, the original props are simply unavailable. They get lost, sold, or destroyed and have to be recreated. I see no issue with a new prop being tweaked to make it read better on screen or to add more detail for close ups. On screen, most, if not all, of these changes go completely unnoticed. It causes no continuity issues. We're just a particularly observant bunch, so, we notice these things. I, personally, love having all the different versions.
As for how he got the compass, we saw that, clear as day, in the new film. Tia Dalma never said that she was the originator of the compass, just that Jack had to barter with her for it. It obviously came into her possession at some point and Jack had to make a deal to get it back. Just sounds like an untild story to me, not a break in continuity.