Following up on my post I found this article, which addresses the question of drafting overagers.
Why overage players could be found money in the 2017 NHL Entry Draft
This is the key point in the article. Higher chance of success but lower ceiling.
"In the article, he came to the conclusion that drafting overage prospects beyond the 2nd round was a draft inefficiency, in that D+1 and D+2 players drafted between rounds 2-7 became full-time NHL players more often than prospects in their draft year. This line of thinking was also promoted by former London Knights Assistant GM, Jake Goldberg, who was recently hired by the Arizona Coyotes as their new Director of Hockey Operations.
Although overagers appear to become NHL players more often than those in their draft year, it’s important to note that they tend to have a lower ceiling."
I think the reference made by NYR2k2 is to a post I did. Sometime within the last year Adam Herman retweeted a post from a former OHL official who may now be working in the NHL. I think the original post said that after the third or fourth round (can't remember) drafted overage forwards had a higher rate of success than drafting 18 year olds. I don't think there was a reference to a study just a statement with that conclusion. Unfortunately I can't find either tweet but perhaps someone else can.
In any event I think the tweet makes sense. The point that Amazing K makes is the key. Relatively few draft picks from the fourth round on make it to the NHL as a regular. So if you have another year or two of data on a player's development you would expect to have a higher rate of success than picking an 18 year old. Look at Brad Morrison. 60 points in his 18 year old year and he looks like a very good 4th round draft pick. But then two more 60 point seasons and suddenly the pick doesn't look so good and he doesn't even get a contract offer. The fact that the overage picks selected by the Rangers didn't pan out doesn't how that drafting an overager is a bad idea. It only shows that there is a low rate of success with picks as you get into the fourth round and beyond.
I'm not advocating for only picking overagers as you get into the later rounds but I see the logic of drafting a player on whom you have more data if you feel that data shows a greater likelihood of success than drafting an 18 year who may become another Brad Morrison.