I'm sure someone will correct me if I'm wrong, but I'm not sure as "full tithe payer" is an option in custom reports.
I suspect you'll need to create a report of Melchizedek priesthood holders, then pull up the list of full tithe payers and start checking them off. Once done, count them up. It sounds like a pain, but I doubt if it will take all that long to do. I'm guessing 10-15 minutes.
rmrichesjr is right, the stake clerk is the trainer of ward clerks.
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