It's a close call, but I would beg to differ on this. Section 609(g)(1) of the FCRA says a lender has to provide a credit score disclosure/NTHLA "in connection with an application initiated or sought by a consumer.." It doesn't say "request" or "inquiry," it says "application." Since the term "application" isn't defined in the FCRA, I believe you can look to other regs (Reg B, RESPA) for guidance. If you are not treating your prequals as "applications" under some other Reg's definition and are not providing the other disclosures (GFE, early TIL, etc.) required within 3 days of an "application," then it could be argued you don't have an "application" and don't have to provide the NTHLA either.
If you've already set up a process to provide the NTHLA earlier, then I'd probably stick with it. Otherwise, I might think about this again.
Good luck.
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The opinions expressed are mine and not those of my employer