Corrected entry: In "Friends" season 8, in "The One With Monica's Boots" A sister of Joey named Dina comes to talk to him about the fact that she is pregnant while she is still a teenager. You would think Joey would have said something like "Go ask our oldest sister Gina, she had Michael when she was 16" or something like that, but Gina isn't mentioned at all. One could say that this is a Friends-mistake, but we don't discover it until we meet Gina and Michael in "Joey", so.
Corrected entry: How on earth can an unemployed actor with a non-paying tenant afford a huge, luxurious, two bedroom apartment, complete with balcony and communal hot-tub, all within a few miles of the Hollywood sign? That's the expensive side of L.A., and he'd be very lucky to get that apartment for US$4,000 a month.