I recently found out about 10.2C RFA'S. Yamamoto has played 102 games can be offersheeted but Hughes has played 127 but can't be. How does this work?

Because it’s not GP, it’s pro seasons. Yamamoto has 3 seasons, while Hughes has 2.

See: https://www.capfriendly.com/faq#rfa

So since ELC slides are a thing for CHL/Liiga/SHL players, usually the only way a player becomes a 10.2c is if they’re an NCAA player or KHL player and sign near the end of the season. Which means their contract doesn’t slide, but they also don’t accrue a pro season.