Yes, the "additional code" term in SEUCK games is something like a quality-seal, in the upmost cases, because only then, in my opinion, such construction-kit games, can be really good. When you look at the best SEUCK games so far, nearly all of them uses the enhanced engine and i really like, that these kind of games are getting better and better. The special-edition of "Zap Fight 2" still is my SEUCK number-1 game and a really good shooter on the C64.
About the number of releases for retro-systems. I think, C64 has the most ones, of all the older systems, because when you take a look at things like for example the C64 Scene-Database (CSDB), then really every day, new things for the C64 were released there. This can be pics, songs, demos, games or tools. Unbelievable, how many new and also often really good, new things come out, for the C64. It's really great, having such a computer at home since childhood and now to see, how much the system is coming back to life. I just wished, that for my other favourite retro-system, the Amiga-500, also more good new games would be released, but sadly that's not the case so far.