Hi Mara
I've been a specialised collector of KGVI and QEII stamps for 43 years; the used surcharge in gold with a black background is common in both used and unused, it is part of a set of 3 shown below.

Although there are many minor varieties with the KGVI issues, the stamp with the mark under the nose is either toning or rust, I have seen many stamps with that type on marking on them. And as the scan is very small I am not able to see if any major variety is on it.
The 1941 surcharge is listed in the Australian Commonwealth Specialists' Catalogue as ACSC 223.
Rob