I’m a biologist and, until recently, I had a real yeast lab. Mostly sold off now. It was used mainly for commercial yeast production and private research. I could bore you (even scare you) with all kinds of bizarre yeast biology. In fact, if my wife can’t sleep at night, she asks me to talk about yeast. She’ll be snoring away within 5 minutes, leaving me wide awake thinking about yeast. My best advice to any home brewer is just focus on pitching enough healthy (ideally freshly prepared) yeast. If you’re a dry yeast brewer, fine, double or triple your pitching rate. Yeast manufacturers are in the business of maximising profits not healthy pitching rates for home brewers. You definitely don’t need to count yeast cells, which is actually a flawed 1-dimensional concept in home brewing practice anyway. Microbiology is only relevant to brewing science and commercial yeast suppliers. Brewers only need to focus on pitching enough healthy yeast. And that’s best determined loosely, empirically speaking, using “bucket biology” scaled down to cups for home brewers. Unless serially repitching yeast like some traditional breweries (with famed yeast strains), it’s not possible to over pitch, which is another flawed concept in home brewing. Just bung it in there. As much as you can. You’ll get a more balanced yeast ester profile for a start. My top tip. It’s all about “bucket biology”. Don’t overthink it. Calm down and have a home brew.
Edit: I'm going off on one now. The only reason it would be 'over pitching' for serial repitching brewers is that the brewery's yeast would age quickly if they added much more than absolutely necessary. For all other scenarios, it really doesn't matter enough to complicate pitching rate. Again, bung it in there!