In a few places one finds a reference to the following document:
Barbara Beeton (ed), “TeX and METAFONT: Errata and Changes” (dated 09 September 11, 1983), Distributed with TUGboat, Volume 4, 1983.
This document is said to contain the changes between TeX78 and TeX82 (perhaps differences between the old TeX78 manual and The TeXbook). Thus it represents an important “gap” in TeX's detailed history recorded in
errorlog. For example, it is mentioned in this article as reference :
By studying the log you can see all the stages in the evolution of TeX as new features replaced or extended old ones — except that I did not record the changes I made when I re-wrote the original program TeX78 and prepared the final one, TeX82. [footnote:] Those changes were summarized briefly in another publication for early users .
The first 519 items refer to the original program TeX78, which was written in SAIL [...] The remaining items [...] refer to the ‘real’ program TeX82, which was written in WEB. [...] The differences between TeX78 and TeX82, seen from a user’s standpoint, have been listed elsewhere.
Is this document available anywhere? The TUGboat website mentions it under “Supplements” to the table of contents for TUGboat 4:2 (and elsewhere), but perhaps as it wasn't part of TUGboat itself, it doesn't seem to have been put online.