Call him, he's very personable. My understanding is that he was at the Montreal guitar show on the weekend, but he may be home by now. If you do speak with him, say hi for me.
I don't know when Marc started dating the neck blocks, but if it is like one of mine (eg, 170596, which translates as 17 May 1996) it will be very clear. My paper labels have the year printed on them too, 19__, with the last two digits hand written. Mine were built in St. Thomas where he's been for many years now.
The "Markham" and "1996" seem incongruous to me, I wonder if the "1996" is incorrect, or maybe it isn't the year but a model. (On edit, maybe it means 19-9-6, as in 19 September 1976). Ask Marc.
As for value, I would have the good folks at The 12th Fret in Toronto, or Folkway Music in Guelph, assess it and get Marc's opinion. For what it's worth, no way would I settle for less than double what I paid for mine, not that they're for sale.
I've heard a few older Beneteaus and they've all been very good sounding guitars, as are his current ones. If you do purchase it, you will be more than happy.