I'd also say they are getting underfed. But to whose standards? I wouldn't say you've harmed them by feeding them less than accepted standards by any means, they are just slender snakes who will take longer to reach maturity.

Track a wild ball pythons progress and i'm sure the don't grow nearly as fast as CB's do.

I'd suggest feeding a bit bigger or a bit more often until they get up to maturity size, by then you can scale back the meals, as they will not need to eat as often at maturity.

Awesome collection by the way. I really like the first normal and the lemon blast, nice looking snakes. The last normal is also pretty cute.