I have been able to fight multiple matches between the two without soft resetting. Characters however have different moves for the same inputs between games, so you can win on one screen gameboy, but not the other. This will stall the gameboy that won and will have the other have a CPU controlled enemy in place of the victor. If the same outcome occurs on both (if the same player wins on both game boys) then another match can occur, even if one gameboy's match ends before the other's.