Don't know if IRC answered the question, but I say false. The date you use is the date the rate is set or locked, not the date the loan closes. See the Commentary at section 226.35(a)(2)-3. If the rate is locked at application, the application date is the date you use. The only way you would use the closing date is if the rate floats all the way up to closing, which is typical in a lot of consumer loans (HE loans, 2nds, etc.).
If you want to get technical, I would say even the closing date is suspect. You have to draw docs a couple days before closing, so the rate has to be set then, right? For loans which float until closing, we always used to use the doc draw date as the date for determining when the rate is "set."
The opinions expressed are mine and not those of my employer