Humans count birthdays from when they pop out into the world and seedlings should be the same IMO.
Starting well after it pops up is like waiting till you get your 1st pube before having your birthday. :P
I start counting when it put them into the tent and they go into the 18-6 circle, so quite early, as you can see in my latest reviews for example. Happy Growing buddy
I don't start my week one of veg until the first week of germination is done. So a week from when I put the seed in soil germination week starts the following week is week 1 of veg. Happy
I also asked myself this question and realized that there is no single solution to this question. For myself, I simply determined that the first day is the day when a sprout appeared from the ground.
I count the Days at all, from the Day i start the Seed
In my Diaries, i use the first week (7days) as germination week
and start with day 8 into week one Veg