Details of RFE:Submit evidence that the beneficiary obtained the required 60 months EXP with job duties in the related occupation before PD date.
OCT 2003 to DEC 2005-Company A
JAN 2005 to JAN-2007-Company B
FEB 2007 to FEB-2008-Company C[US employer]-Client XYZ
FEB 2008 to JAN-2010-Company D[US employer]-Client XYZ
JAN 2010 -Present Company E [ GC sponsor]-Client XYZ .

I dont have experience letters with companies A &C and they will not issue any new letters.
Since I have worked for Client XYZ from 2007 using multiple employers, Is it OK to get a reference letter from Client XYZ to supplement my experience or will it cause negative impact on my approval? Is it OK to get reference letters from co-workers[not managers]? If yes, how many notarized reference letters per company?