Coaches are allowed to check any rosters at anytime. If a player has a late 2003 birthdate and is in 6th grade it does not mean they are holdbacks.. Im pretty sure their parents didn't know at 4 yrs old when making school decisions the kid would even like lacrosse or any other sport they tried.
late 2004 parents who think their kids are at a disadvantage against 2003 kids might want to stay in the REC leagues. If you don't want your child to be pushed and compete against the best kids in his GRADE(club ball).
Mid birthdays are no different, either your kid is good enough to play against kids a few months older or younger or not.
Some teams that play each other every year know the personnel of he rosters. Most of the really good and even bigger stronger kids are late to mid days.