There is no requirement for the form of documentation you should use for counteroffers. As long as you have documented the file in some way that will show the actions that were taken that is fine. I would recommend that your note to the file be something that well documented with the date, time, person making the verbal counteroffer, the counteroffer terms, and any other pertinent information. From what you’ve said it seems your process is fine.
Keep in mind that if the applicant doesn’t accept the counteroffer then you are required to send a AAN within 90 days of the counteroffer. You can send a combined counteroffer/AAN form when making the counteroffer and then you would not need to send a second adverse action notice if the applicant does not accept the counteroffer. A sample of a combined notice is contained in form C–4 of Appendix C to the regulation.