There aren't any "G" sockets out there currently. I think it's a generic Gx code on there - I've shopped a lot at Sears and the old just "G" code was on pre-nickel-only plating sockets.
Regardless those are still all Danaher produced, which was my point, all Danaher which basically means they are just date codes. Basically all the sockets produced after 2000 have all been the same. Eventually they will be Chinese or Taiwanese (Craftsman sockets in Canada are from Taiwan) but probably still Danaher produced. I'll have to look if the impacts are still marked GK even being Chinese, I would hope not but they might.
Really? All 79 codes Danahar used over the years Danaher has been a tool provider are "just date codes'? What about the several times D sucked up another company and continued using the code as they have done several times? All within the 22 years since they bought the first Craftsman supplier? Do you see the discrepancy?
Even for just the G class code, why the need? and why for a random number of years? Far more likely a shift from one plant to another.
If you think about it, I rather doubt Danaher is the deciding factor here; these are made under contract to Sears. Part of the contract will include things like marking the tool to indicate origin, just as they assign a three digit model number to power and other serialized tools for individual companies. Several other major suppliers did the same for the tool codes, such as Western Forge, and again with significant overlaps.
Up until about the mid sixties, individual markings were used for each maker. Why the change to multiple markings for some makers? The mid sixties marked a major move to conglomerates like Danaher sucking up the competition, and the need for Sears to keep track of different plants.
Why? Consider the warranty. Sears would want to know who made what where, and may have even required the supplier to eat part of the warranty costs. If all Danaher wanted was to mark tools as coming from them, one makers mark would have sufficed. no need for 79... If a date code it would have made some sense to the patterns. It does not.
Maybe a picture will help you see what it really is; and note the several times they continued the prior contract companies markings, and also the couple of times they were clearly imported tools...: