[tex-k] Why write_ln is used before final_end in tex.web?

[Karl Berry]

    with the "last newline" problem.

Although (I believe) your specific questions remain unanswered, I did
just post a message from DRF with related information about the original
sail and score systems, which he had written when we researched your
question for Knuth. Maybe it will help you somehow.
https://tug.org/texmfbug/nobug.html#ttynl