Can only assume you had a good turnout at your 16's
Don't disagree that some existing players will miss out, some of them across all the junior grades and all clubs didn't have the quality.
Did you get a chance to go to the other clubs trials? What were the number of 14's and 16's there?
Some U16's think they are capable of taking that leap (and some of them are good enough to be there)18's seems to be a strange age group with many U16's wanting to play up and some over age players also looking for a chance.
Some of the overage players either know or think they aren't good enough for 1sts but still want to play and so are happy to go and be an overage player.