Do the file date/time coincide (or basically coincide) with the date in the filename?
Are the files in a particular directory tree (rather then scattered all about)?
You potentially could have some "ambiguous" dates in there, that could meet both the MMDDYYYY & YYYYMMDD criteria.
If you can
visually identify the files already in the right order (YYYYMMDD), separate them from those you want to act on.
So if you have a directory of files, if you sort that directory by date, & you have a group of files that you
see are dated correctly - the filename's "date" & the date of the file directory entry coincide, then they're already done.
Either don't select those particular files, or move them (temporarily) to a directory outside of the folder you want to work on.
Likewise, using a file manager or
Everything (a GREAT utility for finding files/directories), select only those needing a name change & drag them into BRU.