One of the hardest things to deal with is the accelerating loss of documentation of these old systems. Unless you are lucky, you end up spelunking around weird and not very safe looking URLs looking for redbooks or specs, or, like some medieval historian, trying to figure out what X said by reading some commentary or rebuttal produced decades later that mentions X.
Case in point: in the late 90s I was a user of a product called SNAP-IX, that aimed to convert between SNA/terminals and TCP/IP client server. It was produced by a small UK company, Data Connection, that then got swallowed up and repurposed and ultimately eaten up by some cloud company, and all the documentation, manuals, specs, and knowledge evaporated. Somebody somewhere might have a pdf library, but you'll never find it. They had kept that product going for 25 years. Pfft. Gone.
Case in point: in the late 90s I was a user of a product called SNAP-IX, that aimed to convert between SNA/terminals and TCP/IP client server. It was produced by a small UK company, Data Connection, that then got swallowed up and repurposed and ultimately eaten up by some cloud company, and all the documentation, manuals, specs, and knowledge evaporated. Somebody somewhere might have a pdf library, but you'll never find it. They had kept that product going for 25 years. Pfft. Gone.