I know that everyone is asking a question every three posts, but here's mine: when does "alternate paths" in a game mean that we can no longer cover it?
For instance, many of the Eleventh Doctor games that have straight-forward narratives still have alternate dialogue paths that you can come across. Characters will say different things to you if you have various items, for instance. Is that enough to call the game invalid? If not, how much has to be variable for it to be uncoverable?