I think that your initial suspicions were correct about the CRT! The question really is whether it was 'reverse engineered' or an 'authorised' copy. I suspect the former.
There's no printed labels, serial numbers or anything to be seen anywhere and you can't see much of the neck itself. I'm not in a position to take any more photos for a week or more (complicated), but I will in due course.
It would be informative to find a Toshiba data sheet for the tube, but Japanese CRT data has always been difficult to come by. Richardsons (see:
www.rell.com ) used to have a great library of these things but I've lost my contact there. I don't even think that they have any interests in CRTs these days.
Best regards,
Paul M