The NMLS number is required when the mortgage is presented for signature and as discussed in a previous thread the existing mortgage has already been presented for signature therefore the NMLS would not be needed when using an existing mortgage.
(g) Name and NMLSR ID on loan documents. (1) For a consumer credit transaction secured by a dwelling, a loan originator organization must include on the loan documents described in paragraph (g)(2) of this section, whenever each such loan document is provided to a consumer or presented to a consumer for signature, as applicable:
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The opinions expressed are mine and they are not to be taken as legal advice.