I don't think the "instant vac pump damage if turning brop backwards" is universal, or even common.
Recently when searching for a vac pump which is STCd for my plane (to keep around as a spare) I read some details of a fairly common pump which was rated for 50 hours of reversed operation at cruise RPM!
One may ask how on earth could that be achieved; apparently it can be achieved if fitting a pump to the "wrong" engine in a twin. Or, in a case of a vac pump failure (perhaps in a twin but not necessarily), one may have to fit the "wrong" kind of pump as an emergency measure.