A good idea.
I was going to do something similar for IVV members but the problem is that where people are members of more than one clan it is a lot of extra work.to do so
It would have been easier if each challenge had an indicator of which clan the member was playing for.
At present the only way to do it is for each members to keep their own stats or to set up an excel file and transfer the individual stats at the start of each new month.
Again a lot of work for very active clans.