iirc 30 years back when I worked for Madison it was very common for people to use a 600 Ultegra as it was about £31 whereas an XT Short cage when available was £36 or £37.
At that point Madison (from what I can remember) only had a Shimano delivery every 3 or 6 months by ship, they had to wait to fill a container so if they had a run on something you could easily wait 3-6 months for it to come back into stock.
The biggest difference between the 600 Ultegra and the XT Short cage I think was the seals on the jockey wheels.
12-28 was probably the most sold cassette size at the time, at least in London as most people used their bikes on the road as well.