Unique number in target / personate image target

Hi there,

This may be an advanced question hehe.

I want to send my customers a AR surprise but I'll have to put a unique number(client number) on the image so I can recognice their name and use it in the app. Example: Client 1 gets the image target with number 02134

If he scans it unity connects 02134 with the name John

So the app will say hello John. What i thought that the solution was: - Making image targets for all my clients (250)  

But vuforia doesn't she enough diffrents 80% of the time you get the correct name

20% of the time he's finding another name because he uses the wrong image target. What is the best solution?

I want to personate my AR message