Region names are initially derived from either
It appears that recorded regions are always named after the track, not the active playlist in that track.
These are not audio files, but regions that represent the full extent of an audio file. Every time a new recording is done, or a new file is imported to the session, a new region is created that represents the entire audio file. This region will have the name of the track/playlist/original file, followed by a "-", then a number plus a dot and then a number.
For recorded regions, the number will increase each time a new recording is made. So, for example, if there is a playlist called Didgeridoo, the first recorded whole file region for that playlist will be called Digderidoo-1. The next one will be Digeridoo-2 and so on.
For imported regions, the region name will be based on the original file name, but with any final suffix (e.g. ".wav" or ".aiff") removed.
Normally, whole file regions are not inserted into tracks or playlists, but regions derived from them are. The whole-file versions live in the editor region list where they act as an organizing mechanism for regions that are derived from them.
When a region is inserted into a track and playlist, its initial name will end in a version number, such as .1. For a recorded region, if the whole file region was Hang drum-1, then the region in the track will appear with the name Hang drum-1.1. For an imported region, if the whole file region was Bach:Invention3, then the region in the track will appear with the name Bach:Invention3.1.
If you copy a region, it initially shares the same name as the original. When you perform an operation modifies one of the copies, Ardour will increment the version number on the particular copy that changed.
You can rename a region at any time. Use the region context menu to pop up the Rename dialog. The new name does not need to have a version number in it (in fact, it probably should not). Ardour will add a version number in the future if needed (e.g. if you copy or split the region).