Pretty easy. You should not

go to work for B company before you received the receipt of the H1 transfer application. So the issue is when you started to work for B company and when you got the transfer receipt? The receipt date should be earlier than the starting date with B company. Maybe the reason is that your H1 transfer application was sent out before your renewal application got approved. For such case, you should attach both receipt (renewal and transfer) notices not only approval notices. Those documents should cover those gaps.