I believe it would be Gobl 1685m.
Gobl 1677 does not contain "PF" in the
obverse legend.
Gobl 1700 is a possibility but it has four distinct
types: no mark,
wreath,
wreath with dot inside and
star. I do not know of a
Gallienus "
Restitvt orientis" (Gobl 1700) without a mark. Admitedly, I am not certain how Gobl 1685m would be distinguished from a Gobl 1700 no mark.
As you observed, Gobl 1685m can also contain pellets in the
exergue. Gobl classified one pellet as Gobl 1685m(2), two pellets as Gobl 1685m(3) and three pellets as Gobl 1685m(4).
Hope that makes sense, as it is unlikely to simplify things.