I don't know if this gives a clue to you Matt:
If I look in Documents ► JRiver (which is not where I have directed MC to do backups) there are folders for MC 23, 26, 28, 31.
I will delete 23 & 26.
Now the curious part of this is that 28 has folders created in Feb, Oct, Nov of 2023, and that is all. I do not know how these were created. And why so spasmodic?
Those folders are 67 to 70MB in size.
If I then look in M-Drive
M:\1.1 MUSIC - JRiver\Media Center 28\Library Backups (which is my desired location)
there are backups going back to May 2023, but nothing for Aug 2023! Eh?
Furthermore (refer to screenshot attached), there is a folder for each month May to Dec 2023 (minus Aug), but also 3 to 6 individual backup folders from Oct, Nov, Dec which have not gone into the specific month folder.
These are all 67-70MB in size.
The two manual backups that I have done (Nov 2022 at the top, and Dec 2023 at the bottom "before 31") are both more than 3x that size at 248 to 252MB. The Dec 2023 one ( two days ago) has thumbnails. I am now going to do another backup of 28 without thumbnails to check the size.....standby.....yes, it's back down to 70MB.
I don't actually understand what those thumbnails are, if someone might be able to explain please.