When buying old dirt cheap lenses for use in modern cameras with the help from adapters, the flange focal distance is always limiting factor. The article about flange focal distance lists the different flange focal distances of various standard mounts along among other data the number of mount converters produced (a figure that I take must refer to official converters). It is of great help when I need a fast reference during online auctions. However, a lens with longer flange focal distance than the one of the target mount does not guarantee that an adapter is available or even possible to manufacture. There may be protruding levers for aperture and focus control, limiting mount size or other features that makes the design of an adapter an impossibility.
I've been (unsuccessfully) looking for a comprehensive list for what lens mount can be converted to another without using extra lenses, losing infinity focus or having to modify the old mount.
Today I'm keeping my own list of possible lens mounts, but there are so many lens mounts and combinations that I can't keep track of them all.