In [1] there's a bug report about ALTER TABLE ... ALTER COLUMN SET
(n_distinct = N) not working for partitioned tables. Of course, you
need to use n_distinct_inherited for partitioned tables, but the docs
don't say that.
I went through a few iterations of the wording to make this clearer
and landed on the attached.
David
[1] https://postgr.es/m/18916-985c04e9b5bed12b@postgresql.org