That is good news, indeed, as I am trying to prove two people. Is there a place you would recommend to read more about this type of record? Do you know if the originals are indeed at the PA State Library?
There is a good article in The Western Pennsylvania Historical Magazine, Volumes 1 - 3. Google Bookshelf has it.
Don't forget the 1790 and 1800 Depreciation Tract Censuses.
I believe that the records are in the Pennsylvania State Archives in RG 17.