Since PUBLISHING problems are still occuring, since I further need help,
and since the thread where I posted this question is now closed,
I am in the obligation to post about it anew,
and I guess I'm in the right section.
David, I did what you said me to do :
"Go into your Cpanel
click on file manager
click on public_html
and you will be able to see all your file names.
check that the file name is exactly spelled as in your link
or vice versa."
I went there, and saw that I didn't name the troubled pages identically.
Slowly, in order not to make any error, I re-typed the cPanel correct names into BV.
So : I re-named, re-saved, and re-published every troubled page.
Crossing fingers, I went on the web,
so that I could check if everything went back correctly...
Once again: NO, it didn't.
Always a "404 Error" and "Requested URL Not Found" message...
I have to say I feel more than lost.