Well that did not exactly work.
Upgradepkg displayed as if it was doing the job but:

it did copy the old 2.3.2 package to /lib correctly
seems like doinst.sh did not run correctly
it did not remove the 2.3.4 files & links or do new 2.3.2 symlinks
it removed 2.3.4 from /var/log/packages and wrote the 2.3.2

so, upgradepkg failed to upgrade correctly to a previous version.

Had to fix the mess by hand, will upgrade to pkgtools v10.1 and see
if that does a better job.