My understanding is that those are the ringcode from the GD-ROM however it does not indicate a different version of the game, just slight differences in data in production so don't expect a newer more updated version of the game just because of a different ringcode. The game version is indicated seperately in the filename.
For example the following should be exactly the same game version but the data may vary slightly between the two production batches, so 6S and 10S are both in the collection for archival purposes only, the game experience should be the same:
Crazy Taxi v1.004 (1999)(Sega)(US)[!][6S]
Crazy Taxi v1.004 (1999)(Sega)(US)[!][10S]
However the following would indicate a different updated version of the game as the version number changes:
Mortal Kombat Gold v1.001 (1999)(Midway)(US)[!]
Mortal Kombat Gold v1.006 (1999)(Midway)(US)[!][6S]