Except that is contrary to us lacrosse rules that a lot the "age based" ( not grade based) tourneys play. In your example 9.1 is the cut off with us lacrosse and most age based tournaments. In your example kids in other regions of the country are playing with 2019 kids even when they are in 2020 grad year due to 9.1 being the cut off.

Dec 1 is not the us lax cut off.