We have always been a next day availability bank,
The regulation simply does not contemplate making the funds available on a same day basis. (Consider that in 1990 when the regulation was fully phased in, many banks could not reflect same day deposits on their teller screens.) The only possibilities it contemplates are "next day" or "delayed" availability.
Accordingly, I don't think your disclosure needs to reflect "same day" availability at all. If it does, your change is a little over 23 years late... Seriously, I would not bother and if a third party said it was necessary, I would ask for some support for that advice. If they could provide it, I would send notification of the correction, but it's a "no harm, no foul" situation.