A Flyertalk member reports that they were short points for redeeming a Priority Club hotel reward. This person called and asked if they could go negative in their account, since they were really close, and the agent just gave them a 1000 point bonus to make up the difference. No cost, and better than buying the points for $12.50.
Another member says they were allowed to go into the red in their Priority Club account.
Starwood definitely bonuses people the few points they’re short an award, though the last time I queried this was a couple years ago.
American has told me that if you’re within 500 miles of an award they’ll let you book it.
I’m not an expert on the Lufthansa program, but I recall that Lufthansa Senator members are (or were?) allowed to go negative in their account by something on the order of 180,000 miles!
I’ve never systematically compiled a list of airlines and hotel programs that do this, I’ve never really needed it (and when I’ve been close to an award I’ve always been able to transfer points into an account from another source or quickly earn the miles). But it’s an interesting feature nonetheless. I’d love to hear from anyone with experience here.