Some of the initial information detailed at the beginning has been updated due material I found and your kind contributions, below (in black) is what remains unchanged and in blue what has changed since. Points 3 to 6 remain unchanged without any new information, interesting information to gather is in red.

The Shimano Deore m700 group set was the second bike component set made for off-road/mountain bikes. In the USA, this group set was initially available for sale in January 1983, appearing in some MountainBikes, Ross, and Specialized 1983 model year bikes. Mass adoption of this component was slower than for the Suntour Dirt group. Components likely would have been manufactured before January of 1983, but I have not seen or been shown a 1982 stamped component. Components have a stamp code in the form (YM) for Year (G, H, I, J, K, for 83-86), Month (A-L, for Jan-Dec).

1. Earliest Shimano published material showing the Deore XT group set is a January 1983 large format brochure, detailing Shimano Touring Components. Apparently, Shimano made similar large format brochures early in other years. For example: Jan. 1983 BMX, Touring, Racing, February 1984 BMX brochures, before that there’s online posters or ads about components, or single parts like the 1978 DuraAce, 1980 DX pedals, 1981 DX levers.

2. Earliest date code I’ve seen for a m700 component is HB for a February 1983 date set of MC70 Cantilevers.

Thank you all for your contributions to this forum and Cheers during the Holidays.