Great, thank you for figuring it out. That might come handy in the future.
As for the folder name, I think that are the coordinates of the overmap itself, with the last digit being the Z-level of that map. Based on your folder: LEVEL 0, -2’???, 1’???
Also, if I remember right (from an other, older topic - might not apply here), the relative (submap) coordinates are split up to represent 12x12 tiles each instead of 24x24 ingame tiles (as one overmap tile measures).
Edit: I’ve found the older topic I’ve mentioned… You can find the submap explanation in the “Step by step guide to get the coordinates” spoiler at the end of this post.