ALSO, the Aussies tried to put the whole history of the rifle onto the Butt. This is why you will run into Lithgows with wonderful woodwork, perfect barrels..... and Butts that are beat half to death.
My Lithgow is a 1918, but the Butt has 5/33 and 5/44 stamps as well, indicating that it was back to the factory for work in May of 1933 and 1944.
After the 1944 rebuild (new wood) it developed The Damned Crack again and so they painted it red (not to be shot) and then sold it for junk. Two bits' worth of Acra-Glas, tiny bit of careful work on the Forestock and it shoots WELL under an inch.
Your Gas Escape holes are a safety measure and were on all SMLE rifles. They are one of the reasons that a separated case is MUCH less dangerous with the Lee rifle than with a Mauser. The Lee allows the escaping gas to blow straight out of th rifle, almost at source, while a Mauser routes it through the action, which is why Mousers sometimes blow the bottoms out of magazines.