HrHJ (2017) has altogether 3 coins depicted with
palm branch in
field and no one without! On one coin the branch is present but difficult to recognize.
It is well known that coins for
Commodus from
Nikopolis sometimes have strange and unusual depictions that you can't find somewhere else.
My working hypothesis is that the earlier coins have
had the branch in
field. Later, possibly because of technical difficulties, the branch was omitted.
Jochen