A few years back, IMDb cast listings were pretty much watertight. If you’re wondering “Who’s that guy, where have I seen him before?” then all you needed to to is catch the name of the character he’s playing, and you could be almost sure that he’d be there, and be almost sure that unless it was an advert or something he’d be listed in the thing you remember him from too.
Now IMDb is so incomplete you can’t even be assured of major parts, let alone bit parts, being listed. Is there anybody else doing cast lists that my be better, or at least on a case by case basis be better than IMDb? There’s Wikipedia which will sometimes have a cast listing for a show that IMDb doesn’t, but only the main cast, but anything else?