You are exactly right. At the end of the month, I use the total from my statement to calculate my XIRR. In between statements, I use the "Account Value" on the Summary page. Adjusted account value factors in expected charge-offs, but it does not appear on the statement.
So to calculate XIRR I'd take the balance under account total (available cash + committed cash + outstanding principal) on 5/31/2016, include any deposits, and then the same account total balance on 5/31/2017?
You would use your beginning balance on 5/1, then any deposit or withdrawals, and then your ending balance on 5/31. Example:
5/01/2017 $1000 (beginning balance)
5/15/2017 $250 (deposit)
5/31/2017 -$1300 (ending balance in negative)
=XIRR(B1:B3,A1:A3)