Not doubting your memory Rory, but I have two RTs, both of which have a “5” stamped on the front of the receiver. Neither is stamped EG - at least according to my records - I didn’t pull the forearms again. (One has a “4” and the other has a “5” stamped on on the bottom of the barrel.)
Always doubt my memory!
Need to pull out all my prewar 99R's and 99RS's and check the front as well. Everyone I remember has an 8. But never took notes on them.