I'll tell you that I tried to run this down a few years ago. I reached out to several compliance vendors, the ABA, and others, and the general consensus was that you could provide orally and stop the 30 day clock for incomplete applications in 1002.9(c). Once you had a complete application, the 30 day clock would kick in. I could not find any support for this in the Reg or commentary and wasn't provided any, but everyone in commercial lending was pretty sure it was true.
My 2 cents are that regardless of business or consumer, an applicant that provides an application that meets the definition of an application under Reg B, but is not a completed application due to items in the applicants control needs a written NOI within 30 days if they still haven't provided the items and the app hasn't been otherwise dispositioned by that time. I could find almost nobody that agreed with me, at least within earshot of a commercial lender.