Copying modified files only

Two options:
(1) If - after copying them to the flash drive - you cleared the archive bit of the files on that drive, it's easy: xcopy with /a parameter.
(2) If not, the best way seems to open each folder on that flash drive in Windows Explorer, set the view to detail, sort on creation or modification date and select a whole bunch of files (the upper part) by selecting first the first, then the last with shift pressed, then drag and drop those file back to their original location. That's one operation per folder.

By the way, would it harm to copy the unmodified files also? Only if some of those files were edited on the original PC. If any of the files were edited on BOTH PC's you've got a problem, whatever method you do.

Kees

Thinking out loud here. What if when you modify it on the second computer you changed the name of the file, like put a M or 99 in front of the file name when you save it on the flash drive. Then you could sort them by name and only copy them back. But I guess then you would have to go through and change the name back and delete the original unmodified file off the first computer. But maybe that will give you some ideas.