make sure his draft status says undrafted and his rights aren't owned by any team when you create him.
This is the biggie. I made about 7 or 8 players who aren't yet in the game and put them in the game, and since I couldn't change the rights off Anaheim (Which I later figured out how, just click randomize on the biography screen when you're making the player then move the rights to "none"). None of them were in the game, I went about two seasons then noticed Jones was playing for Anaheim. I went to their roster and I noticed numerous very strong prospects that I had created on that team.
Wasn't that big a deal because none of them had developed anyway (Only Jones was above 75, and he was at 77). I guess the game has a secret attribute that effects how fast a player will develop. Shinkaruk always jumps to 85+ overall within 2 seasons but guys like Barkov and DeAngelo (2014) never develop.
I fiddled with the ratings, made both Barkov and DeAngelo 5 stars, Barkov 65 overall, DeAngelo 55 overall, hoping Barkov would develop quickly and DeAngelo would be up to 65 or so by his draft year. Not the case, in the 2017-18 season Barkov was
only 74 overall and DeAngelo was only 57 overall. And of course by the time they reach 20 they have to play in the AHL and when you're that low an overall the game just puts in non-NHL contract free agents to take spots on your AHL team which ensures unless you micromange your AHL team (Very difficult to do with the high frequency of injuries), you can't get them ice time, which stunts the development of most of the high potential low overall players you draft.
Only notable guys who seem to develop quickly, MacKinnon, Ristolainen, Sam Reinhart, and Shinkaruk. Everyone else doesn't start developing untill they reach the AHL and they don't develop big time there unless they have great seasons which is impossible (You can get them ice time but no chance they have a great season that skyrockets their overall) unless you play the AHL games to do it.