More info: after further testing, the built-in iPad photo app will not consistently retain the photo sort order, even IF all three date flags (created, accessed, time last modified) are sequentially one day apart.
Scenario: I alter the date flags on a group of four photos on my PC, move those to the iPad, sync, and they are in date order on the iPad. Then -- after moving *other* photos to a different photo album on the iPad and syncing, the first four photos are no longer in order. But I didn't change those after the initial sync. The order changed by itself.
Putting them back in order requires this procedure:
(1) In Windows Explorer, move them off the photo sync folder (designated in iTunes)
(2) Sync iPad, which then deletes the photos from the album
(3) In Windows Explorer, move them back to the photo sync folder
(4) Sync iPad
This puts them back in order, yet they weren't changed. This should not be required and is a cumbersome procedure.
If the iPad photo app has specific sorting behavior, this should be documented *by Apple* for *all* conditions. If there are exceptions or bugs, this also should be documented. Apple has the source code. It should not be left to end users to determine this by trial and error.
One of main purposes of an iPad is photo display -- it is not a niche use. Using a 3rd party photo display app should not be required for something basic as sort order.