From what I recall (though I had to do some digging for names/years/etc. and some of this has already been mentioned):
-Wings signed him to his ELC after his first camp, but then his stock dropped a bit from his OHL playoffs and WJC play the season after he was drafted
-He struggled his first year in GR
-Had a pretty good opportunity to establish himself early the 2nd year when MacDonald was recalled to cover for an early weeks long Osgood injury, but was outplayed by #5/6 guy Jordan Pearce. IIRC, McCollum would then get demoted to Toledo until Osgood was basically done for the season.
-For the rest of that year, GR basically rode Pearce into the ground to try to make the playoffs, which is why McCollum got recalled to sit on the bench before he had his memorable NHL debut.
-It kind of seemed like the Wings gave up on him after that, but kept him around as organization depth since his ELC slid a couple years
-Had another less than good year shuttling between GR and Toledo
-Started to improve during the lockout year, though the be fair, those Griffins teams were also a lot better
-Despite his improvement, he was usually still behind another prospect goalie that was playing even better (namely Mrazek and Coreau)
I did think maybe he'd get a start after he had that solid period against the Lightning in 2015, but that was it for the NHL for him other than dressing as a back up here and there.