I was reading through old posts about how the Pottermore wand quiz works (here), but don't understand why they chose to base the wood type on eye colour, a trait we're most proud of, and what path we choose. Why isn't it, at least largely, based on the Celtic tree calendar? In fact, based on my eye colour, I can't get the wand wood of my birthday. . .

Also, for the date of birth, that seems kind of random, since it assumes we're using a Gregorian calendar. Some other calendar system probably has me born on an odd day, not an even day. I would understand if it was month, such that it's based on when the tree starts blossoming (or, again, use the Celtic tree calendar), or something like that.