IMO Appendix A of RESPA provides guidance. It refers to the name and address of Lender for Section F, and for line 202 the "amount of the new loan made by Lender".
If there was one note/loan and you immediately participated 20% liability to the affiliate, then it would appear to be OK. If there were multiple loans then I believe the affiliate finance companyis correct.
Why wasn't it caught before? Examiners are good but there are many things to look at during an exam. Their priorities may have been elsewhere.
Integrity. With it, nothing else matters. Without it, nothing else matters.