Owners cannot "hold" extra MLB assets (players + waiver picks) after the cut down date. This means that if an owner keeps 20 players and has 6 waiver picks (one acquired via trade), their worst pick disappears effective at the cut down date. This also applies to extra MLB assets acquired during the draft; if an owner that kept 20 players and has five waiver picks trades an MiLB pick or a prospect for a waiver pick or MLB player, their worst waiver pick disappears effective at the confirmation of said trade. An owner that has made all of their waiver picks and thus has 25 MLB players cannot make any trades during the waiver draft that would give them more MLB player(s), even if Yahoo would accommodate the trade (by, say, placing a player in an NA or DL slot).