Putting the Millenium Falcon in the PT is the definition of universe shrinkage. I know we're supposed to say that everything they put in the PT was wrong, and everything they didn't put in should have been, but this is one of the things the PT got right.
I assure you if they had found a way to shoe-horn the ship into those films the same people clamoring for it now would be complaining about how it was nonsensical fan service.