I have a 32gb s6. All the photos in the stock gallary are our odd order. Listing photos from 7 to 8 months ago as taken today or yesterday. Really making things hard to find.
If they're being listed my modified date order, anything you do to a picture changes its modified date to "now". If that's the order the pictures are in - latest ones that you did anything to first - they're correct for descending date order.