OGM exception on deed containing multiple parcels

I have a question regarding an old deed conveying multiple parcels (5 parcels listed by number) in Pennsylvania. The deed lists them one by one numerically and underneath the last parcel there is this clause:

"Excepting unto the grantor, their heirs and assigns, and successors a one-twelfth interest the oil, gas, and minerals, in on or upon the above described premises"

My question is does this except a 1/12 in the ogm's on all the parcels or just the last one described in the deed. To me this is very vague and one could argue that the exception only applies to the last described parcel. If one were to make an exception on ALL parcels, it should have been stated that the exception was to be on all parcels conveyed in this deed, etc.

Has anyone ever came across this type of vague language before in researching deeds and what was the final determination?

Dear Lowflyer,

If it were me running title, I would credit the Grantor with 1/12 on all lands described and conveyed.