Hi Rob,
Alfons obviously included the instruments he'd sold in his serial number list, but as you say, like this particular Double Six, the appropriate info on it now belongs to you! I therefore trust YOU don't object to me using these details and I hope the new owners of his other subsequently sold examples feel the same way.
I really don't know where these very precise production figures come from. For example, I've seen 315, 350 and 450 authoritatively stated for the Marvin, while Burns apparently manufactured either 20 or 200 Split Sound six-string basses, depending on which 'accurate' amount/account you believe! I can cross-reference enough research material to arrive at educated estimates for most models, but I can't claim the results are exact and they usually contradict the quantities quoted elsewhere! This was one of the reasons why I decided a serial number database was well overdue and I just wish I'd started it a lot sooner.
I appreciate your suggestion regarding a revised, updated and significantly expanded edition of The Burns Book. It would be nice if it was indeed that easy, but as I've previously stated on here, these days such a project simply isn't a viable proposition in terms of time, effort or possible financial return. The market for guitar books is now appreciably smaller, even for those concerning the more mainstream makes and models, so potential publishers tend to steer well clear, which sadly means all the additional information I've avidly accumulated over the years won't be put to good use.