ARD 3.3 loses Serial Number when Cloned

Question

I work for a school district with a 1-to-1 laptop program. We use ARD to allow the teachers to preform tasks on their student's computers, without having to go to each computer individually.
I thought that we had a bunch of individual ARD licences, in other words I thought each teacher had their own licence and that was why we took the serial number out of our images. However I found out this year that we actually have a site licence and every teacher was entering the same serial number. So I decided to simply put the serial number in the image, so the teachers don't have to look up and enter the long serial number.
Unfortunately, I found that when I put the image on another laptop ARD asks for the serial number. So I tried applying the image to the laptop that I made the image on in the first place, using the same imaging technique I used with the other laptops, and ARD works fine.
My next step was to image another laptop (which did ask for the serial number) and compare the two. I compared the /Library/Preferences/com.apple.RemoteDesktop.plist files, they are identical. I took a quick look at ~/Library/Preferences/com.apple.RemoteDesktop.plist, it looks the same but does not contain any reference to the Serial Number.
Can anyone tell me if there is a way to clone the serial number between machines? Or does anyone know for sure what is causing this problem?
We have 2 images, 10.4.11 and 10.6.3, both are doing the same thing. We use Deploy Studio to make our images, and we used a combo of Deploy Studio and Net Restore to re-image the laptops. We are using MacBooks.
Thank you for your help.

Answer 1

Hey Dave,
First off, yes I have checked our licensing and we are covered for multiple installs with the same serial number. And I have done a t test to make sure there is no problem with ARD complaining about the same serial number being used on the network. All of this was done months in advance of starting the new batch of images.
Secondly, yes I know the serial number is encrypted. Apple would be foolish to not encrypt it. My point is that you can see the encrypted data in the preference file and if both laptops have the same encrypted strings then it stands to reason that they have the same serial number. In other words, the cloning process is making a good copy of the installed serial number.
So the bottom line is that I know the serial number I have will work on multiple machines (if it's entered manually), I also know that my image is good and the encrypted serial number is not being corrupted in the re-imaging process. The real question is what does ARD use to decode the encrypted serial number? Is it something physical, the laptop serial number perhaps? Or is it another file somewhere that has been corrupted in the imaging process? If it is something physical then it simply cannot be done and we're back to having the teachers enter their own codes. On the other hand, if it is a file somewhere then maybe I just need to adjust the imaging process somehow.
Thanks for the help.