Based on a small sample...

by Hoot , Diversityville, Liberal-sota, Monday, August 06, 2012, 09:46 (4494 days ago) @ Charles

The paper boxes in hand contain dies with the following dates...
No date
1965
1968

The earliest set in a plastic box, T-lock, is dated 1973.

Assuming they are all in their correct boxes (pretty good bet), we're narrowing in on it.