The date codes indicate a certain week in 1966, which suggests that they were all manufactured at about the same time. Why are there two date codes? My best guess (and again, this is just a guess) is that the vertical date codes indicate the date the tubes were first labeled and warehoused, awaiting shipment to a customer. At this point they could have been sold to almost any customer. But perhaps at a somewhat later date, the tubes were selected to be sold to the US military. They were pulled out of the warehouse, the JAN code was added and the date indicates when this happened.
In the end they were all manufactured at about the same time, and I suspect that the later date codes, 6648, would only have had meaning for government bean counters. But again, I'm just guessing.