Did you check discogs? That's usually where I start if looking for matrix
info. I just got a UK first of Meddle, cleaned it but haven't listened to it yet.
PS: check the 1975 US reissue, it looks like that might match yours.
Sometimes, you'll get a mongrel, that has the same stamper or deadwax
info as one identifiable release, on one side, with something completely
different on the other side, that doesn't seem to match a particular pressing.
For example, I just got yet another Monarch pressed copy of LZ1 that has
the AA 'RG' info on side 1(corresponding to a US first) , side 2 is something
else entirely!