Bass are often stocked a year before the bluegill in Northern climes, upon the recommendation of state DNR's, for this very reason, so they have time to get a head start and can be big enough to control the bluegill when they're stocked.
I live in Nebraska and everything I've read has suggested the opposite. Stocking BG first, wait for at least one spawn, then stock your LMB. This way the BG get themselves producing and still provide a nice forage base for the LMB.
