Greetings,
I would suggest that you check with The Thunderbird Registry.
There are over 58,000 Birds of all years registered. Yours may have been registered before and he may have some info on it.
You can contact them here:
Thunderbird Registry - Contact Form
If you do Facebook they have a group you can join and ask there also.
https://www.facebook.com/groups/tbirdregistry/
or CTCI:
https://www.facebook.com/pages/Class...976374?fref=ts
You should join CTCI if you are not a member.
CTCI - Classic Thunderbird Club International
There have been instances of some oddball codes and there is some conjecture that they were typos when the code was punced into the data plate.
HTH