TUSB9261: Serial number authorized values

Part Number:TUSB9261

Hello,

I'm editing the USB descriptors info using the TUSB926x Flash Burner tool.

It works well for the Manufacturer and Product fields, but I have some troubles with editing the Serial # field:

It works for some values ( for example with 64 'A' ) but it doesn't for others ( for example with 64 'B').

What is the authorized range for this field?

Besides, is there any command line tool for production purpose?

Thanks in advance.