Austen Lennon

I have one of the above and I have seen one other of these Gibson TG-0 tenor guitars without a serial number. I believe it is a 1960's guitar. I work on a lot of guitars and know that this is true Gibson.... does anyone know any stories about why there are a few 60's tenor guitars without a serial number? I am selling this and the proceeds will go to an Animal Charity so I would like to get the right information.