Date of Manufacture, Gardner Propeller

[rcgrunt]

I have a Gardner propeller. The info stamped into the prop reads DES. 491 (Xed out), SER A 40551, and A.T.C. 710 (Xed out). I know the Xing out indicates it was deemed not airworthy. I have 2 questions I need help with:
1. How can I figure out the prop's date of manufacture?
2. What do the initials A.T.C. stand for?
Any help is appreciated. Thanks

[Dave]

ATC stands for "Approved Type Certificate" and was used before the end of WW1. See this explanation.

To my knowledge there is no correlative list of Gardner serial numbers with date of manufacture.