There is no direct requirement in 3500.15 for the disclosure to me signed. However one can argue there is an implied one because 3500.15 states the disclosure is to be given in the format of Appendix D and 3500.15 does not give an option to change it.
The regulation says a person must give the disclosure not later than the time of the referral, not prior to the referral. If you are the lender and require a particular provider then you can make the disclosure at the time of application or you can make the disclosure with the GFE.
I would be giving the AfBA with the GFE, or I wouldn't be using the affiliate.
Also, other than a homeowner insurance affiliate, why wouldn't these affiliated settlement service providers be on your particular provided disclosure or on your bank maintained or approved list? Either way, they would still require the AfBA disclosure.
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The opinions expressed are mine and they are not to be taken as legal advice.