wolfywatts: It would be useful to know what ball to use for say..warming up, practice or ranked,tournement etc games. I have quite a few last ball in the sleeve that I dont know how much life is left in them and regret using one playing a ranked game as when its used up and you have to play with standard balls until the end of the round, which could be costly.
You might want to consider a rethinking of your POV.
IMHO, it doesn't help much to know the status of any "last ball" because - no matter how many shots are on it - it may not last for the round in question due to a wayward shot OOB or into water. Thus, if "it may be costly" in an important round, you'd have to prepare a second ball (or even more) to prevent the unwanted use of the Starter ball. This may be done by advance purchase or by buying on the fly.
Consequently, we can use last balls only where it doesn't matter, in leisure rounds. If it vanishes in a solo round, we can always quit the round, while in MP rounds it would be a fun subject in the chat and a challenge to complete together with your friends.
wolfywatts: I know some buy the same balls [...]
I do so, but not "religously". It's based on efficiency because any change of ball would alter the shot dynamics and impair my game. Furthermore, changing balls is unwanted extra work. I have had three balls in six years, Starter, Tour-SD and L33 Cally, and I don't care about the growing collection in my inventory ;)