I read from another thread that it's: EXP ## MONth(day & the first 3 letters of month NVC sent your petition to Juarez) 2011A. So since NVC told you they shipped it June 6, your reference # is EXP 06 JUN 2011A. You just have to go through all the petitions sent from NVC that day and search for a Juarez one.
No, the number you got on your NVC letter is your case number.
ALSO, CALL NVC and ask for:
1. Beneficiary number
2. invoice number
*you will need these #s (along with the CDJ############ on you NVC letter) to fill in form DS-260.