Mercedes E300 loaner question

2017 loaners are getting slim. I finally found one where I’ve got the sales price down, compromised on the money factor, got the fees in line, but dealer now says PenFed won’t let the certificate be used on loaners-only new. PenFed closed today. Is this correct? Could it be dealer is considering it a non-new car, or PenFed is? Anyone heard this before? Past posts indicate certificates will work.

That’s technically still a new car. The car waa never titled so dealer shouldn’t have a problem.