Yes, but remember, you cannot fly on the day you APD'd. Say it's a 4 day trip, 1-4 Aug. You could put your APD on Aug 4 and drop the whole trip, then pick up a trip on 1-3, but not on Aug 4.

BUT, once you've used your APD, it's gone. Just because you only used one APD day, the others do not remain for another use, they all go when you use one APD day.

Oh, and we used to get 5 PAID APD days too! You got paid for the trip you dropped, but again, you cannot fly over any day(s) you APD'd.