I, personally, use zero added sugar in any form. I don't eat sweets, except for the less sweet fruits. I don't add maple syrup or date sugar or anything else to foods. I know that is not your question though, tpund. I would answer your question with another question. Why, since we have an inflammatory condition, would we consume added sugar, which is an inflammatory substance, in any form? As the ideal at least.
I can't find anywhere in the book or online that OMS sets out a specific amount of added sugar that is okay or is the acceptable limit.
Here is another thought. I love to say that, "I stuff my face with nothing but health food." That bit of hyperbole makes me feel great. We have a condition where, among a host of other factors, our mitochondrial function is impaired. There is research that shows mitochondrial function impairment over time contributes to disability progression. Optimum nutrition supports mitochondrial function. Why consume empty calories at best, inflammatory ones at worst? Why displace food that is helpful with foods that are potentially harmful. It's a bummer we can't do the things other people do. I think about all the crap I ate when I was younger - I guess I front loaded my full life-times complement of pleasure foods and now I have to get to work nourishing myself.
If you still want a hard and fast number of how much added sugar you can eat in a day, why don't you check out Dr. Greger's (of Nutrition Facts and How Not to Die fame) three minute How Much Added Sugar is Too Much video on Youtube: https://youtu.be/zbfx6qRPidA
I personally think all his videos are helpful (though, boo, he doesn't like fish because, like Dr McDougall, he is vegan) in my opinion and act as a pretty great resource behind Jelinek and OMS.