Yep, pretty much. : )
If 77 is game-breaking I might change it, but IMO it's fine if 79 is bad.
so far 77 feels pretty balanced, and 79 likely has some niche uses anyway since you only get 3 7s.
Two of the ribbons require your deck to be composed entirely of primes. In this case, you can't use 77 but can use 79.
