A couple of examples of variations and Lot number configurations.
Lt numbering changed in years past. The OD M-16 mine used the method from the 50's, with manufacturer and date. The Final assembly manufacturer in this case is designated by the 3 digit Alpha code LOP (Louisiana Army Ammunition Plant), which is standard in the U.S. for defense contractors to use. Each contractor is issued a 3-digit code to stamp or paint their Identification on the item. The blue M-16A1 uses the current Lot numbering method which incorporates the year into the number, in this case IOP is the manufacturer (Iowa Army Ammunition Plant) and 77K is the year and month of final assembly and loading, K being November as it is the 11th letter in the alphabet. The final digits in the LOt number comprise a particular lot that was manufactured that month.
The problem with your research as approached here, is that all you have to work with is the loading contractor and date. As you can see in the sectioned M-16 mine, there are many components that go into the mine. These are all manufactured by the lowest qualified bidder. These are then assembled into subassemblies, which come together at the final Assembly/loading plant where they leave complete with explosive contents, most likely minus the fuze.
