I think that your patch offers too much detail, like from which relations the statistics are extracted. Anybody who wants to know that level of detail probably has to read the source code anyway.
How about adding a simple remark, like
--- a/doc/src/sgml/ref/pgupgrade.sgml +++ b/doc/src/sgml/ref/pgupgrade.sgml @@ -837,6 +837,8 @@ psql --username=postgres --file=script.sql postgres all statistics, such as those created explicitly with <xref linkend="sql-createstatistics"/>, custom statistics added by an extension, or statistics collected by the cumulative statistics system. + Transferring optimizer statistics works regardless of the old cluster's + major version. </para>
<para>
That would work too -- my goal was just to resolve confusion.
