I’m guessing the 'blind' method looked something like using one of the early graphics tablets to trace routes or tap control points on a paper map according to a sequence displayed on a text terminal, with no graphical feedback to confirm the vector data during input.
in 1988 i was doing an internship at a company designing ship propulsion systems. they had a CAD computer with with a huge screen and tablet. not sure how old that device was or how expensive but i guess in '85 the technology was not far away.
digitizing blind at that point would mostly be used because it was cheaper than getting a graphics capable computer.
using a projector instead of a screen would be enough to devise a system where the digital image is shown on top of a printed map. so when they came up with that idea they probably already had most of the pieces they need to make it work.
