I'm still a bit confused on this. Maybe it's the TVMaze system which is a weird hybrid of listing characters and stars.
Most recently, tonight on Arrow. Colin Donnell is credited, albeit not by character name. But he doesn't play Tommy. Or rather, he plays Christopher Chance playing Tommy. The actor playing Christopher Chance, Wil Traval, also plays Christopher Chance without a mask.
But we know that it isn't Wil Traval wearing a Colin Donnell/Tommy Merlyn mask. It's.. Colin Donnell playing Christopher Chance playing Tommy Merlyn.
It doesn't seem like there should be a third hybrid character. Spoilers aside, it's still the character of Christopher Chance. Playing a character that has been dead for five years on the show.
It doesn't seem like there is any factually accurate way to present the casting information in the TVMaze system. You presumably can't leave Colin Donnell off the credited cast list. He's credited onscreen. But you have to list him as a character. Listing him as Christopher Chance would bring up the character photo of Christopher Chance/Wil Traval. But he's not playing a new character. Donnell is playing... Traval playing Christopher Chance playing Tommy Merlyn, the latter who is played by Donnell.
I suppose you could create some weird non-existent character, like "Tommy Merlyn at Oliver's Trial". That seems awkward, a bit spoilerish (not that that's a major concern: I understand), and likely to spark an edit war as someone look at it, says, "WTF", and changes it.
Does that make sense? :)
Anyhoo, thoughts?

