I think the whole purpose of being able to reserve your photos, so that you alone can transcribe them is of prime importance to this whole BG project. You are the one photographing them. You have seen them with your own eyes; and it is quite possible you have taken notes for hard to read stones. If you are allowing others to transcribe them, just because they are in a geographical proximity to the cemetery, it is absolutely ludicrous.
Photos most of the time cannot detect what the human eye can, so if you are allowing others to transcribe your pictures then you are probably going to get inaccurate information.
Personally, I've been working on a very large cemetery, photographing in small pieces, in a systematic method that allows me to keep track of where I've been. Unfortunately, the GPS coordinates have not been the greatest and have misplaced stones well away from their actual location. I've "reserved" my photos, so that I can transcribe them one at a time and subsequently adjust the pins on each and every headstone into their correct location in the cemetery, based on my photographing methodology. If others get into my photos, they don't know that the pins are misplaced and are not going to be unable to move them to their correct location. It would make more work for me to correct them and it would make it virtually impossible for anyone using the app to locate a headstone.
BG fix this issue! If I want to allow others in a "group" to transcribe them, then I should have the ability to direct which transcribers I want to have access to the photos. They should not have access just because they live relatively close by.