When the game is never released, unfortunately. Such was the sad eventuality which befell Mega Man Anniversary Collection, the Game Boy Advance game which had been formerly known as Mega Man Mania before an ironic change to accommodate a celebration it would never be a part of.
The following video from Game Informer shows footage of the colorized version of the Game Boy Mega Man titles in all their unreleased glory.
Truth be told, between the two collections (and not counting X), this was the one I was most looking forward to, given that the Game Boy games were a bit more rare than their NES/Super NES/PlayStation counterparts. Hopefully someday Capcom will "find the source code" (I have my own theory about that, but it can wait for another time) and give these worthwhile titles, considered by some to be superior to their technologically superior NES cousins, another chance at life.
And by the time that happens, maybe they should just toss in Mega Man Xtreme and its sequel as well.
News Source: Protodude's Rockman Corner