Can you help VK2IXV?

TO ALL AHARS MEMBERS:
 
Are you able to help Hermanus  (VK2IXV) with the following query?
 
"Hello John,
I wonder if any of your AHARS former PMG employees knows
about the meaning of the markings on PMG Morse keys.
I have seen so far on PMG Morse keys:
I have come across several S123 markings on PMG keys as follows.:                                                                                                        My PMG key:                         S123 6 C2044-40                                        Ron McMullen’s key #345: S123 7  C2644-40                                        Ron McMullen’s key #501: S123-8  C2344-40                                      Ron McMullen’s key #625:  123-6  C4875 46                                        The 2 keys of Kees VK1KVS: S.123-6 C.3423 42 and S123-6  C3984 44   

You see that S123 is common amongst all the above PMG keys.

Was it a PMG catalogue or warehouse order number? Would somebody know please?

​Thank you and 73, Herman Willemsen VK2IXV Kiama NSW"
 
I have been in contact with Doc, who is unable to help.
 
Please reply direct to Hermanus if you can help,
hermanusw@gmail.com
 
John Elliott
VK5EMI