I dug a bit deaper into the IAU listing of comets and fount the following:

The nature of an object can further be indicated by an initial prefix. In
particular, such prefixes should be applied in cases where comets have
possibly been misdesignated as minor planets, or vice versa. If necessary,
the prefix A/ would precede a comet designation that actually refers to a
minor planet (or asteroid). For comets the acceptable prefixes are P/ for a
periodic comet (defined to have a revolution period of less than 200 years
or confirmed observations at more than one perihelion passage) and C/ for a
comet that is not periodic (in this sense), with the addition of X/ for a
comet for which a meaningful orbit can not be computed and D/ for a
periodic comet that no longer exists or is deemed to have disappeared.


Looks like 75P = 75D no longer exists.

Bob Elliott