I'll jump onto this thread with an odd "cheat" experience with Galaga.
I tried that thing in Revision 1 of Galaga where you don't shoot the leftmost enemies and all enemies eventually stop shooting at you.
When I started the game, I inadvertently hit 2 players. I played through both players, concentrating on the player 1 game and just letting the second player get killed pretty quickly each time.
When it was time for high score entry, my second player game with the crappy score was listed right below the player 1 score, above much higher scores.