> Wither your build after pulling failed or was incomplete, or the way
   > you displayed the doc string is wrong.

I just run

git pull

I did not compile or install. I just went to
lisp/gnus/gnus-art.el

I tried  run

git pull

again, found out there was an error. after a couple of intents it
finally worked, now I can see the new string.

So most likely my pull an hour ago, was not complete. (Which reminds me
how much I dislike git, a pity that git was preferred over
mercurial...... :'(