Philipp <p.stephani2@gmail.com> schrieb am Do., 20. Juli 2017 um 23:32 Uhr:

The docstring of `print-gensym' says:

When the uninterned symbol appears within a recursive data structure,
and the symbol appears more than once, in addition use the #N# and #N=
constructs as needed, so that multiple references to the same symbol are
shared once again when the text is read back.

OK, so you could read this as "the numbering is only used for recursive data structures". But I don't understand why; it seems equally appropriate for non-recursive data structures.