So this is lil bit complicated. I was with company X, got my H1b exended till Dec 2013. I left this company to join Y, who initiated visa transfer, and got RFE. In such a situation if Z offered job, can I use only approval notice I 797 of X only, and paystubs, offer letters other supporting docs from both X and Y to make a transfer to Z.
Yes, they can use X’s petition and other documets from X and Y for the transfer. You should also use Y’s transfer receipt to show that they did file the transfer in timely manner.