I finally paid if off. She's all mine free and clear.
And as they were supposed to, the lender promptly sent me an official looking "Notice of Intent to Release Preferred Mortgage Lien" (or something like that).  This Notice came within days of their receipt of my final check and it has no evidence that the USCG has seen it or done anything with respect to actually releasing the "recorded" mortgage. Question: Do I need to send it to the CG in order for them to release the lien? I'm inclined to think so.