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.
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