Well the tag is 40 bits, and there is a class of HID cards with 40-bit IDs (so-called Casi Rusco format). I found a press release that states HID would distribute Casi Rusco products circa 2000. My card dates back to that particular year.
So I believe it’s alive and well, just very old and not very common anymore. Hence the PM3 saying it’s invalid/unsupported and yet knowing it’s valid at the same time, possibly if the two different parts of the firmware that spew out those messages were coded by two different people, one of whom included the possibility of 40-bit IDs just because they once existed.