I tracked down a four decade old TeX file Knuth used in a lecture from 1981 and restored the printed version.
On a whim I tried to find the handout Donald E. Knuth used in an intro course for TeX back in 1981, which I watched on YouTube. After finding a few specific search strings I came across files generated during that course in a big archive of the first Stanford A.I. Laboratory, where I found much more than I had hoped, including all the original TeX files for the course, which can still be processed by TeX today, after some adjustments.