@rgrandy shared a couple of the incorrectly-aggregated images with me, and it turns out that the photographer stripped the images of all standard timestamp tags (!!), and added Metadata Date, which is an XMP tag (that I’ve never seen in the wild before: I suspect it’s from Lightroom).
@bdillahu , @Adrian-Ng , if you can send me some incorrectly aggregated images, it might be another case of a simple tweak I can make, and then you don’t have to fight the de-duplicator anymore.
This fix will be in 1.0.0-beta.4 (which will be released soon).