ok - i'll answer my own question here. yeah, it's true. the front headliner has to be in before the rear goes in in order to get it to overlap. what a kerfuffle. well they're both in now and aligned right...
my next challenge, oh mighty headliner gurus is the damn fir-trees. where there are correct sized holes to go in, they go in just fine. however, on the front headliner above the windscreen there are little black clips that appear to correct the hole-size.
for the life of my, i can't get the xmas trees into the black clips without them going 'ping' and coming off... any pointers?