This can has a 3/8 inch tab where the key used to be.  This makes it the oldest of the flat top cans, circa 1930. There is a code stamped on the top, 192D. This can has never been opened so I am describing it as new but as seen in the pictures it is bent, scratched and rusty.  This is the oldest can of tennis balls that I can find on the internet.  The latest patent number on the can is from the 1930's. I found it last week at a garage sale in Amsterdam, NY. The can says APPR. U.S.L.T.A. on the picture of the ball with Championship above the word Pennsylvania.  It is thought that Pennsylvania may have been the first company to produce a can of "pressure packed hermetically sealed fresh" tennis balls.  The words in quotes appear on the can.  It also says "always fresh, fast and playable" and " a new ball from center to cover" .  It list six points of superiority: 1. Balanced construction and absolute uniformity of product, 2. Thick rubber center inflated with nitrogen gas assuring long life, 3. Patented "V" shaped center seam-an excellent Pennsylvania feature, 4. Select virgin wool felt cover constructed specially to resist wear on hard courts, 5. Latex seam and vulcanizing of felt to rubber positively eliminates cover center separation, 6. Hermetical sealing in metal tubes under pressure maintains built in liveliness indefinitely. CAN HAS NEVER BEEN OPENED or TAMPERED WITH, NO HOLES IN TIN,  WHEN CAN IS SHAKEN YOU CAN HEAR BALLS RATTLE INSIDE - STILL INFLATED - CAN IS STILL HERMETICALLY SEALED.