Yeah most are gonna start counting veg at sprout. Too many variables to define veg starting at any other point, but it doesn't really matter. The size of your plant when you begin flowering is more important than how many days of veg it’s been. The plant doesn’t care how old it is, unless it’s an auto I guess.
Same for flowering. Day 1 is the day you flip to 12/12. Some will say to count from when you see pistils but again, lots of variables there (what if you didnt see the pistils the day they first appeared?) Maybe ok if you have just a couple plants and you’re constantly eyeball-f***king them, but impractical when you have a large flower room with many plants.
It’s really just about consistency. You know definitively the day it sprouts above ground. you know the day you flip to 12/12. Those are concrete. Anything else is more guesswork than fact.