Hi Joe -
First Welcome to the board. The first T206's were printed and inserted into packs well into 1909. Player selection and artwork for the set took place early in 1909 and the first printings and distribution happened in early summer.
I don't believe there is any significance to the date stamp on your card other than it's a cool addition to the card by a collector over 100 years ago.
If you can post a scan as there are several collectors on the board like myself that enjoy the various stamps found on vintage cards. You never know, there may be more out there just like it.
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