You make it so hard to help you, what with the syntactically erroneous code,
the hand-wavy minimum reproducible example, the verbiage, and the transposition
of up versus down (C-v is scroll-up, not scroll-down).
I don't believe the code I posted was syntactically erroneous at all. It might be the older style for defining advice, but it is still syntactically correct.
As to hand wavy minimal reproducible example, I find it far easier to read than what you have presented, plus your code seems heavy handed with multiple calls to force redisplay when all that was actually required was to add the 'update switch to the call to window-end.
Yes, I did refer to scroll down when talking about both C-v (scroll-up-command) and pgDown (yes, formally it is called 'next' in Emacs, but on the keyboard the key is labelled pgDown). However, this is really just another example of how terminology has changed. At any rate, I'm sure my 'verbiage' made the intention clear. Besides, the direction was irrelevant - the issue existed when scrolling in either direction and most people these days talk about scrolling down when moving to the end and scrolling up when moving to the beginning.
Should you find any of my future posts as frustrating, you can of course just ignore them. I really don't. mind
emacs -Q --eval \
"(dolist (f (quote (scroll-up-command scroll-down-command))) \
(add-function \
:after (symbol-function f) \
(lambda (&rest _args) \
(redisplay) \
(princ (format \"wstart = %d, wend = %d\n\" (window-start) (window-end)) \
(function external-debugging-output)))))" \
--eval "(save-excursion (apply (function insert) (mapcar (apply-partially \
(function format) \"%d\n\") (number-sequence 1 1000))))" \
--eval "(progn (scroll-up-command) (scroll-up-command) (scroll-down-command) \
(scroll-down-command))" \
--eval "(kill-emacs)"
emacs -Q --eval \
"(defun tx-window () \
(redisplay) \
(princ (format \"wstart = %d, wend = %d\n\" (window-start) (window-end)) \
(function external-debugging-output)))" \
--eval "(save-excursion (apply (function insert) (mapcar (apply-partially \
(function format) \"%d\n\") (number-sequence 1 1000))))" \
--eval "(progn (scroll-up-command) (tx-window) (scroll-up-command) (tx-window) \
(scroll-down-command) (tx-window) (scroll-down-command) (tx-window))" \
--eval "(kill-emacs)"