Evaporation CONCENTRATES the CYA even higher (the same amount of CYA still exists, but is in a smaller volume of water after evaporation) and then adding new water DILUTES that same CYA to exactly the same value it was before evaporation. The net effect from evaporation and refill is NO CHANGE in pool chemical concentration (not just CYA, but CH and everything else).

Having CYA near 60-85 is fine if you are willing to keep your chlorine level up at around 8 ppm FC (minimum of 5 ppm FC), but you will be using a lot more chlorine every day by doing that and I suspect that using pucks you aren't keeping your chlorine that high. That means risking getting algae. You can avoid that by using weekly algaecide (PolyQuat 60), but that's expensive. The main purpose of BBB is to maintain the pool inexpensively.

Believe me, if there were an inexpensive source of slow-dissolving solid chlorine that didn't have CYA in it (or calcium either), then I'd be using it as you are right it would be more convenient, but there isn't. With a pool cover, however, one can cut down the chlorine loss per day such that you only need to add liquid chlorine (bleach or chlorinating liquid) every 3 days instead of every day.

Richard