When working with a collection agency the more accurate information you provide about the account(s) the better it  will improve collections. The information should include:

Full Name, Address, Telephone number of the debtor
Name of debtors spouse
Debtors occupation or last known occupation and phone number
Names of relatives, friends, and references
Summary of any disputes
Date of last transaction
Cellular phone, fax, pager numbers
Nick names or aliases, maiden name
Has their mail been returned?