How do I ... determine when a campaign member's status changed?

How do I ... determine when a campaign member's status changed?

Is there a way to tell when a contact's member status was modified for a given campaign?

I'm using two Campaigns to divide contacts up into two piles - one for receiving a welcome by email and the other for receiving a welcome by postcard.  The email and postcards are processed currently outside of Zoho CRM.  When done, I update the member status from Planned to Sent.  Rinse and repeat every week.  Now I have two piles of "Sents" and can't tell which week who got what. 

Perhaps instead of solving my initial question, there's a better way overall.

Thoughts?