So I made 3 new pages (none have any likes yet). Then I did the vanity name thing for one of them -- worked fine.
But... when I went to do the same thing for the other 2 pages, FB told me it's not possible + that it would be possible in the future. I don't know what that means.
I thought it maybe meant to wait a day or so. But now I did wait 2 days, and it still says the same thing.
Again, none of these 3 pages have any likes and they were all ceated on the same day.