Great news: all issues prior to the current one are now publicly available for download as PDF. That's a treasure of now 39 years of TeX articles.
Only the access to the current issue is restricted and is for TUG members only. Until earlier this year, issues became publicly available one year after publication. That was relaxed after a successful open ...
A copy of the document “TeX and METAFONT: Errata and Changes”, originally distributed as
a supplement to TUGboat 4:2 (1983), has been scanned from the possibly only remaining
original, and posted with that issue on the TUG website. (The original files no longer
exist, or at least cannot be found. The scanned copy is a bit fuzzy, but it's complete
-- all 47 ...
The main difference is that the \ninepoint you defined was using a 6pt script size, but tugboat uses 7pt, copying a few more tugboat definitions gives
@\penalty via @@5 b=10 p=500 d=250400
from a modified document
in retrospect it seems obvious that for Udo's examples, we should have turned off tugboat.sty's hyphenation exceptions (and anything else that might have affected line breaking). None of us thought of it. Sorry.