I think Randy is making two points:
1) If you have the six pieces of information included in the link you provided, you have a completed application for TRID purposes, so your question phrasing of "without an application" doesn't make sense; and
2) Why do you need a cover letter at all (but even if you do, it could be as simple as "Here's the Loan Estimate you requested".
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Jim Bedsole, CRCM, CBA, CFSA, CAFP
My posts - my opinions