RPMs ended in 1989. If they are present on the post 1990 coins then they would be doubled dies. (which this one is not) But the two know so far are these:
Now there are 4 of them known. 1999-S 25¢ Pr PA WDDO-001 http://doubleddie.com/186364.html If you have time, check this one out. It is the only DDO on the States series that does not involve the earlobe.