With the latest update of the NES and Famicom applications on Nintendo Switch, the first noticeable difference has actually appeared. Previously, most of the differences were just in the language. This time, though, the Japanese application got one more game that is not available on the NES application.
The November update for the NES Nintendo Switch Online included the following games:
(SP) Gradius: Gradius but, by default, it loads a save state in which you are fully powered up and start on stage 5 (if I recall correctly)
Metroid: Regular NES Metroid, password functionality works the same way to the point that you can crash it with the right code.
Mighty Bomb Jack: Another regular NES game.
TwinBee: Regular NES TwinBee.
You can see each of the games in action in the video below:
In Japan, though, they got the following:
(SP) Gradius: Same special version as above, just in the Japanese release.
Metroid: The Famicom Disk version of Metroid. This includes enhanced music and a save file system similar to The Legend of Zelda.
Mighty Bomb Jack: Same as above, just in the Japanese release.
TwinBee: Same as above, Japanese release.
(SP) Mario Open Golf: A special version of the Japanese release of NES Open Tournament Golf. This version starts by default with a save data where everything is already unlocked.
As you can see, the Famicom Nintendo Switch Online application actually got one more game in the latest update compared to the NES version. The biggest reason why this happened is because Mario Open Golf is quite different to NES Open Tournament Golf in its contents.
The first difference and main reason why there’s no SP version is that NES Open Tournament Golf has everything already unlocked by default. In Mario Open Golf, Japan is the only course available at the start and the rest need to be unlocked. There’s also the fact that the Japanese version has a few more courses available and the overall game is harder. Similar to Super Mario Bros. 2, it was one of those games that Nintendo thought it would be too hard for players outside of Japan. In this case, they did release the same game but with a simplified and lower number of courses.