The way to "pick up" flying on reserve is to answer the phone when scheduling calls you offering a trip last minute. There are rules governing the order in which scheduling is supposed to call people, and of course there are always rumors that those rules aren't always followed. If you can prove you got skipped over an NCC may result in getting credit for the trip, but it's difficult to prove without a lot of snooping around on flica and crewtrac. A new guy with low hours is fairly close to the front of the line to get called, once the standing available list has been gone through.

As for dropping an entire month of reserve and still flying... It's a silly thing to argue over If you're really that new and drop too much, just answer your phone when scheduling calls.