Actually I have not idea!
The Keycaps section would seem to be a good place - but who would think to look there?
A new thread in Group Buys is not really appropriate, as it is not a new group buy.
And anyway, the few with erroneous sets is generally only one key duplicated, and many if not most people would have posted here.
BTW I put some of my blue Tau Hao onto my KeyCool and took it outside for a photo shoot. I noticed that some of the legends are a bit smeared, and the plastic on some keys is not consistent (the right Shift, for example). I hadn't noticed either of these while indoors, either sorting through the keycaps or fitting them on the keyboard. Might just be under brighter light it shows up.