I do sometimes go around looking for other sales when I know there has to be one, thanks to sites like CAG. But usually I expect the dashboard or the deals page that the dashboard links to let me know about stuff like that. I usually don’t tab over to the Microsoft store on the extreme right of the interface.
Luckily, I don’t have quite the same problem owning stuff on PC, since I don’t usually get the humble bundles. I purposely didn’t get the Hat in Time one, for example, precisely because I thought it would be more fun to play it in the living room on Xbox, going after achievements along the way.