End of the story...
Through the original italian dealer, where the guitar was bought in beginning 2007, we succeeded in contacting Taylor, submitting them S/N and questions.
Their "official" answer is:
it's a transition model, when we passed from 3V to 9V battery, for some time it has been used an endpinjack with a small board and the battery fixed inside the body, untill new housing on the bottom has been ready. So it seems a "rare bird"...
Well, it sounds happy end
