Since that Namcot Collection is out in Japan and Namco Museum Archives overseas, here is one game not included in the compilation library.
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Pac-Mania is the only NES game not released by Namco.
Released to the Arcades in 1987 and ported to the NES in 1990, the main reason why it is NOT in the compilations is because it was originally by Tengen and not Namcot. This shows that Namcot really missed a title to port.
What is infuriating that it was NOT Licensed by Nintendo and Namco didn't even re-release the game unlike how they did to Pac-Man in 1993. There wasn't even a Super NES port of the game either.
After the Nintendo Switch came out in 2017, there was a Plug 'n' Play by AtGames titled the "Bandai Namco Flashback Blast" which included 8 NES ports of Namco's Arcade Games. One of them being THIS GAME, available at Wal-Mart in place of The Tower of Druaga, which is included in other stores.
This product was infamous for abusing Bandai Namco's own reputation and its misleading features because original gameplay trailers and the back of the box show full arcade emulation, while the actual product has NES ports of the included games. The sound also doesn't work on many TVs.
There was also another Plug 'n' Play by MSI Entertainment titled "Namco Classics Vol. 1" which contained this port of the game along with Dig Dug II and The Tower of Druaga.
UPDATE 5/7/2022: Pac-Man Museum + is out this month, which will "finally" contain the game.