H1B Transfer without I-797 copy

My Employer A had filed a fresh H1B petition for FY 12-13 and it was approved however I left Employer A and now Employer B wants to transfer my petition and have sent all the documents to USCIS. I only have the receipt number and do not have the I797 approval notice with me. Can my H1B still be transferred? What if Employer A files a withdrawal Notice with USCIS, can the visa still be transferred.
Appreciate quick help