I would love your thoughts on this conundrum:
I want to source a digital image of a page from an 18th century church register, which is presently stored in a vault in Philadelphia at the Presbyterian Historical Society. (The church however is in New York and remains active to present day.)
The page I wish to source is now imaged on (and probably by) Ancestry, in a collection they labeled Presbyterian Church Records, 1701-1970. This collection includes churches from all over the place, as one might imagine.