There is very little about Barber dime varieties online. CPG has an RPD for 1899-O and that's it for the year. David Lawrence (1991) has a 99/99 but I can't see anything in the plate in the online reference. Variety Vista has a few RPM's, but CONECA (James Wiles) has relegated the rest to the "specialty clubs". Flynn's book might have this one, not sure. You might contact the Barber Coin Collectors' Society via their website, and look through their journal archives. It wouldn't surprise me if yours is undocumented. It looks like an RPD to me.
FYI, I documented in BCCS that there is a third reverse design type introduced in 1900, and there are a small percentage of 1899-P with the 1900 reverse. Yours is the 1892-1899 reverse, but design transition varieties in Barber dimes are fun to look for too.