A relative got the $999 and 35K offer but didn't sign up because at the time the rules said something like register, book and fly 35K to get 1K. She already had a lot of travel booked for next few months that seemed like it wouldn't qualify.

Later the rules changed to read something like register and fly, so she paid the $999K and began the 90 day period. Then she called and asked for credit for a couple flights she had flown a few days earlier, because she would have registered if the rules at the time had made it clear that pre-booked travel would count.

They credited her those two flights towards her 35K with no problem, but they also moved the 90 period back a few days to cover those flights. Not a big problem but be careful what you ask for.