Right you are Kai, of course. I was aware last night that apparent/actual attenuation would affect the numbers, but I didn't think it would be by as much as 0.002 since we were dealing with only a portion of the OG. I was too uninspired (or lazy) to do the math properly, but that's an important difference considering the purpose of this exercise. Cheers!
I was also thinking other (unknown) factors could affect the result so that stopped me from going further. One possible factor being maybe WL833 can deal with a small portion of the higher saccharides better than wine yeast. I know most of these won't get metabolized at all. And a bigger one was this odd fact I found on Danstar's site too. And those wishing to train yeast in their spare time may be interested in this wine yeast which acts very much like a beer yeast. At the risk of getting anyone started on yeast taxonomy....There is one very famous wine yeast that is both POF negative and can ferment maltotriose. It is probably the largest selling wine yeast strain in the world. It is Lalvin K1-V1116. It was used in a beer kit for several years and it was the yeast of choice in a Canadian brew pub for several years.
That threw me, because my memory was telling me that I had used a yeast with a very similar number to that -- a possible relative, if not in fact that same yeast. Which only takes me down all sorts of new roads.
all in all, I think I'll just use bread yeast next time like Kai suggests