The USAH ADM coach training now addresses this directly. They require all youth hockey coaches to take self-paced and live workshop training, and require annual continuing education.
One example here that explains the thought process:
"Birthday bias: Understanding relative age effect in youth hockey"
One example here that explains the thought process:
"Birthday bias: Understanding relative age effect in youth hockey"
https://www.admkids.com/news_article/show/823923