RFE on initial petition

[spidy2581]

My first petition from Employer A was picked up in lottery and was approved.  But before I start working before the mandated date, there was an RFE. Employer A will respond to RFE.  I have a couple of questions on validity of my petition in cap

• Can Employer B file petition for me? Since the petition was initially approved, would it be considered as counted against CAP? 
• Will petition from Employer B valid if Employer A's petition approved or it has no impact?