@dawn16 Hmm... I don't think so. If you want to be very precise and you want to count sets very, very accurate - you should know not only what muscles hit given exercise, but how it changes with different modifications.
1.If you do some modification of a given exercise, let's say you do close grip bench press, you chose close grip for some reason, right? If you know the reason, you should be able to tell which muscles it targets more than a regular grip. Unless you're doing it for no reason. That's a weird situation and I don't know what to advise
2.These are details for a more advanced people.. Even if you count it like you've mentioned before, it'll be fine. But let's count high effective reps (HER) to show that. Assuming that in each set to failure you've got 5 HER. So for bench press with retracted scapula and a bit wider grip you can count it that way:
5 HER for chest, 3 HER for triceps, 1-2 HER delts
But if you do with protracted scapula, close grip, elbows closer to the body it can be counted this way:
3-4 HER for chest, 4 HER triceps, 4-5 HER delts
So as you can see. It's a bit more tricky but still - those are details for more advanced people.
Let's say that you're a beginner who doesn't know much about all those modifications and how it affects the muscles. You don't even know the exact muscles, you know there's a chest, triceps, lats and other back muscles. Maybe heard about traps, rhomboids etc. but what they do? idk. You know that pull ups and bw rows hit similar muscles. And after reading this post you know that you probably shouldn't do 15 sets of PU + 15 sets of rows per week, right?
I hope it makes a sense for you. If not and you've got other questions - go ahead