Well, I can promise you this, it does not see any differences. What it does is very simply dump the complete content from the USB drive into an archive folder.
The only reason I whipped it up (as a BATCH file) was because you told me that during the day you connect to a lot of different PC's. If I know schools, then I have to assume that there are a lot of different versions of Windows involved. BATCH scripts tend to work on practically every version of Windows. For example, the script as it is works on every Windows version from Win2000 to Win7.
Although they can be problematic to setup, those scripts tend to be very reliable...and never nice to look at.
But with all the trouble both you and Deozaan experienced, I have to something about my commenting skills. Ah well, live and learn as they say.
Furthermore, Deozaan is totally right about checking for versions will be difficult (in BATCH), time consuming and error prone if drive names keep changing. Now I know that there are tools/hacks to make sure an USB drive gets the same drive letter assigned, but I don't have the time to look into that right now. Besides that, lack of (my) skills in this department do not help your cause one bit.
Hmmm, now that I think of it, there are BATCH script commands that can copy differences only. Maybe it would be smarter to copy these differences to the archive location first and when that is done create the archive and clean up everything inside the archive folder (remove everything, except 7-zip archives).