How to have the spell checker ignoring URLs and acronyms

Dear Vim Experts,
bored to have acronyms and URLs marked as errors in my LaTeX files I have
looked for a solution. Here

http://www.panozzaj.com/blog/2016/03/21/ignore-urls-and-acroynms-while-spell-checking-vim/

Suggests to add

syn match UrlNoSpell '\w\+:\/\/[^[:space:]]\+' contains=@NoSpell
syn match AcronymNoSpell '\<\(\u\|\d\)\{3,}s\?\>' contains=@NoSpell

in ~/.vim/after/tex.vim but it doesn't seem to work.

:scriptnames lists the file correctly loaded

226: /usr/share/vim/vim82/ftplugin/tex.vim
227: /usr/share/vim/vim82/ftplugin/plaintex.vim
228: /usr/share/vim/vim82/ftplugin/initex.vim
229: ~/.vim/bundle/vim-polyglot/after/ftplugin/tex.vim
230: /usr/share/vim/vim82/syntax/tex.vim
231: ~/.vim/bundle/vim-polyglot/after/syntax/tex.vim
232: ~/.vim/after/syntax/tex.vim

But it seems ignored and all my acronyms are still marked as errors.

I've already commented out all the plugins and still they are ignored.

What am I doing wrong?

I'm using Vim 8.2 on a linux box, Vundle is my plugin manager and I've
vim-latex installed.

Any help is welcome. Thank you.

Walter

PS. Note that to add all the acronyms to the list of known words is not a
feasible option.

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