I have to give some thought to how the snaps made the marks. They look almost like burns in the autopsy photos. So if she laid on them while alive, they'd make reddish marks, but not the purply abrasions; if she laid on the, after she died, they'd make white marks as the pressure pushed the blood (which is no longer circulating) away. They are in odd places- under her ear on the cheek (with the faintest -in some photos- hint of a second mark near her mouth on that same cheek, about the same distance apart as the 2 marks on her back. Most people just see the one mark on the cheek- I do see the hint of second mark on the face as well.
I believe Meyer mentioned that there seemed to be a tiny boat-shaped mark in the center of the one under her ear. I don't recall if he mentioned that all the abrasions had that same mark. If they did, obviously they were all made the same way. I suppose no one ever checked any clothing found in the home that could have had snaps or buttons matching those marks. Of course, this would have had to happen before Aunt P made her evidence raid on the house; she would surely have removed any incriminating clothing.
The marks almost look like cigarette burns in the photo, but I would presume that any coroner has seen such burns on a corpse at least once in
his career, and would have been able to tell what they were. Meyer was also a Medical Examiner, which meant he was also a medical doctor. Not every coroner is actually an MD. Some are PhDs, and some have not gone through medical school.