I don't keep track. All my exchange prints go into a box, and I'm glad to have them, and all my postcards go into another box, and I'm happy to have those as well. I don't know what prints are from what round of what exchange. When there is an APUG gathering at my apartment, we pass the boxes around, so everyone can see what other APUGgers are up to.
Some of mine have gotten out late, and I'm sorry about that, but sometimes life intrudes. I keep a list of everyone to whom I owe a print, and they all make it out eventually. I suppose that some people "owe" me a print, but I don't know who they are, and I'm not too concerned about it. I participate in the exchanges mainly to challenge myself to print for other photographers, and if I get some nice prints in exchange, that's a bonus.