To the OP's point, I've taken NR regularly in these doses:
1) 125mg x1/d &125mg x2/d
2) 250 x1/d & 250mg x2/d
3) 333mg x1/d & x2/d
5) 500mg / 250mg /d
7) 666mg / 333mg /d
So basically from 125mg/d to 1g/d. Was any noticeable positive difference with these differing amts of NR? No, not really, I couldn't swear there was.
But I take numerous other supplements, mostly herbal, which would obviously skew subjective opinion. And getting 'clear' for a week or 10 days, typically when I notice a strange feeling, allows reflection and adjustment.
In 9 months taking NR, I've stopped totally three times due to this. Typically, I get some soreness in the upper body/chest/under rib cage area. When it stops, I slowly rebuild the supplement stack, as I said, changing things a bit. Since there zero to no research about the actual health benefits of NR **in healthy humans** (other than raising NAD+ levels), ones own body sense has to be the best guide at this point. And so for me, at this point, anything strange, and I pause.
As others say, I wish someone would come out with definitive advice as to dose and real benefit (not just NAD+ levels), just anything really to use a guidance, but it appears that the powers that be either don't want to, or lack sufficient data to make such recommendations.