I think it used to be
2016 rules wording: - Association-trained players – players who were on another club's books in the same association for three years between the ages of 15 and 21. No club can have more than four association-trained players among their eight nominees on List A.
2023 Rule wording: - Association-trained players who were on another club's books in the same association for three entire seasons (i.e. the period between the first and last official match of the relevant national championship) or 36 months between the ages of 15 and 21.
but like you say, i could be reading it wrong.
@Delphinho ?? Think it was changed to cover Musiala, Sancho etc still counting with the increase in players moving at 16 around the EU etc.