Dating service started in 1964
This will indicate either the date the can was filled, or the date the beer was brewed before, so you have a good idea of about when your can was produced and sold. This applies to the year the label design was copyrighted and it can be misleading.
If you can has the "Keglined" logo on it and if it's from that period, you might be able to read the date code. The earliest pull tab (an Iron City) was sold in 1962. Then it dates from the mid 1970s until the early 1980s. Does it have opening instructions on the side of the can showing how to use a church key?
Schlitz started using them in 1963 and other brewers quickly followed. Most brewers got rid of these by 1942, but a few continued to use them after the war.
By 1967 few brewers still used flat top cans that had to be opened with a church key. Only three brewers that used opening instructions on their cans after 1950; Genesee, Sterling, and Falls City. Aluminum cans came into wide use in the 1970s but the first ones were being sold by Primo and Coors in 1958-1959. A few other brewers including National, Hamms, and Budweiser started using them in the early to mid 1960s. Flat top 15 and 16 oz cans came into use starting in 1953 so a flat top 16 oz can would date between 1953-1964.
You'll find Schlitz cans with copyright dates of 1946, 1949, 1954, 1957, 1958, 1960, 19 and dates afterwards.
Look along the seam for the year on most Schlitz cans.