As for U19/18 group, a significant number of those U19 players are college "unofficial red shirt" or sometimes called "gray shirt" players. In other words, those players are recruited but not ready to play (e.g., red shirt) but have a year of eligibility left due to birth year. Many college coaches have a working relationship with their local DA club and send those players. The coach would rather have the players play than just train and sit out the year. Since these players are intentionally not rostered or have played in any college games, they are eligible to DA.
