DCIM - YYYYMM_xxx folder creation logic

I am trying to backup photos from my wife's iPhone.

Does anyone understand the logic behind when subfolders get created in DCIM? I.e. sometimes there is a 202211 folder, sometimes there are a whole bunch of folders, 202212_a, 202212_b, 202212_c, etc. My problem is that these folders are being created when the copying process errors out, which is making it very very difficult to resume.

She does not have paid iCloud storage and has no interest in paying for it. I appreciate that the immediate response is "just use iCloud" but please, bear with me...

Knowing already that this is a painful process, I plug her iPhone into my (Windows 11) PC. I can access the DCIM folder, with a random number of folders per month. I try to copy these folders. Sometimes it works, sometimes it errors out with either "Device unreachable" or, in one case "Catastrophic error". I sigh, unplug, plug it in again, wait for the folder to become accessible and resume copying.

It's taken me a while to realize, but when the process errors out, and I re-open the DCIM folder, the month folders for the month on which the process failed are newly created and photos seemingly randomly resorted. To diagnose this, I have tried 4 times to copy the folders for 202007. The first time, the iPhone contain 202007_a, 202007_b, 202007_c, 202007_d. When the copy job failed, the photos were resorted into folders 202007_e, 202007_f, 202007_g, and 202007_h. It failed again, they were resorted into 202007_i,202007_j,202007_k,202007_l. It failed again, and the photos ended up in 202007_l,202007_m,202007_n and 202007_o. (I have no idea why 202007_l was not replaced). See the screenshots below for the latest re-sort.

Does anyone have any idea what is going on here? This means that every time I encounter an error, I basically have to start over again with that bunch of folders, since I have no idea which images successfully copied or didn't.

Even when I try to copy an individual folder (202007_n), and it errors, on reopening, all the 202007 folders are resorted, so I have to discard the already copied folders for that month and start again.

Please note: I am aware that Apple will never likely change this, I'm not asking for an easy way of backing up a iPhone to a PC via a cable, however reasonable that request might sound. I just want to understand the current behaviour and the logic behind the yyyymm_x folders - if I can at least understand why they are being created and why (and whether?) images within those folders get completely resorted, I can try and work out the least painful way of doing this.