Technically, by RAW, a 20th-level necromancer can animate and control 101 skeletons/zombies. Every day. Now, leaving aside arguments of whether you would allow that in your game or not, or cheesegaming, etc., the fact is that this would be super annoying for all other players and the DM. But if you came up with some sort of house rule that could combine these creatures into one creature of equivalent power, would you as a player in that game, be happy with that compromise?