As a cache owner, it is most fair, if the statistics, generated by project-gc are fot the period, the cache owner is responsible for.
As I would adopt a cache, I would earn all the logs and all the favorite points for free. Thats not fair because the former cache owner has reached them and it was not me to be responsible for that.
Otherwise, if I would give one of my caches to adoption, my statistics will change and I am "stolen" the Logs in count and words and the favorite points etc.
So the goal has to be to include the time each cache-owner owned the cache in the statistics for that certain period of time.
If you would make it, that would be great and hopefully groundspeak will also lead to that goal.
To clearly manage this fact in statistics will also lead in more adoptions instead of archieve and starting a new cache (even with same listing and old box+logpaper) and could reduse the workload for reviewers a little bit.