106 prospects were invited to the NHL combine this year, ahead of a 210-player draft. Eight of the players invited to the combine were not selected:
I saw just one of them play this year, David Valek (USNTDP), and I wasn't impressed by him, so the fact that he wasn't drafted seemed justified. Mappin is widely thought to be talented but not very hard-working.
There were a few guys who went very high and didn't go to the combine:
31 Mikko Koskinen
35 Kyle Clifford
56 Kevin Lynch
62 Anders Nilsson
64 Reilly Smith
76 Igor Bobkov
When the combine list came out, I wrote on it "No Lynch!" so obviously that one was surprising at the time. A couple others are explainable: Koskinen is an overager and I believe came to the combine last year or the year before. Bobkov was drafted largely on the strength of his performance in the U18 tournament, which was going on at the same time the invite list came out. Clifford I guess teams were trying to keep quiet on him.
The takeaway is that the combine list is a generally good predictor of who the top prospects are, but isn't foolproof.