I scanned many old photos (2000+) a few years back and imported them into Aperture. I spent many evenings arduously updating metadata including the photo date and time (EXIF date). Now if I simply select a photo in Aperture the date will change back to the original date (date the photo was scanned). This doesn't seem to happen to all the photos that I scanned. I can flip thru 20 of these scanned photos and the dates on 5 of them will change and the others will not change. I created a smart album to help highlight when this happens.
I searched around and found lots of issues with changing dates but I didn't find this issue.

I used the “Adjust Date and Time…” menu item in Aperture to modify these dates. Looking at dialog box now I notice the “also change master file” checkbox. I don't remember if I check that or not. When I started correcting these changed dates, I checked this option and the dates seem to 'stick'. But it appears if I don't check this box the dates still 'stick'.

I rebuilt my Aperture database and that didn't seem to fix this issue.

I can correct this issue on the photos that I have identified. But I am afraid to select any of these scanned photos (2000+) hence their date may change.
Assuming my problem is that I never changed the master file when I made all these date changes, is there a way to identify all the photos that have a different date on the master file.

I am assuming this is some sort of error. The date shouldn't change just because I selected the photo, whether or not I originally selected “also change master file”.

Any advice would be appreciated.

I have used Aperture since 2008 and currently on version 3.2.1

Jim