Some sources (like TV Tropes and Pac-Man Wiki) say that Pac-Man Arrangement still has its two-player mode (albeit dummied out). Check if that's true.
Big sprites of Blinky and Inky. These originated from the credits screen of Pac-Man Arrangement (when it was featured in Namco Classic Collection Vol. 2), but this compilation skips the credits entirely for unknown reasons.
Pac-Mania has some debug-related text, including a sound test and a "3D TEST":
SOUND TEST VOICE NUMBER PSG NUMBER FM NUMBER AUDIO 3D TEST
Pac-Mania also has a disclaimer about international copyright:
THIS GAME IS FOR USE EXCLUSIVELY IN JAPAN. THE SALE, EXPORT, USE OR OPERATION OF THIS GAME OUTSIDE OF JAPAN MAY BE A VIOLATION OF INTERNATIONAL COPYRIGHT, TRADEMARK AND/OR OTHER RELATED LAWS SUBJECTING THE VIOLATOR TO LEGAL PENALTIES.
Pac-Attack has an "instant game over" function that can be activated by simultaneously holding Up + Start during gameplay, then exiting out of the pause screen after. This immediately activates the game's game over sequence, even if the player hasn't reached the top of the screen. Strangely, this appears to be a carryover from the "original" mode port of Pac-Attack from Namco Anthology 2 for the PS1, in which the same button inputs activate a similar "instant game over" sequence.
Pac-Attack also lets the player start at level 300 with 0 points if the player holds Right while "Hyper" is highlighted during the Normal Mode level select and then confirming the selection. This secret also exists in the Genesis, Game Gear, Game Boy, Game Boy Color, and PS1 versions of the game, but NOT in the SNES or Gamecube/PS2/Xbox ports.
The Japanese title screen is missing "TM and" as well as "Licensed by Nintendo". The logo also has less shadow behind it.
Pac-Mania has a different logo in the Japanese version, based on the arcade original (along with being consistent with the logo seen after selecting the game). The US version's logo seems to be based on the one in the Genesis port, as there's no hole in the P.
The US version has tips, while the Japanese version has hints.