Number 2......poor selection.
If bought before it was 15 inches long, loss of tancho spot is very common, about nine out of ten.
Part of the problem is cheating on the part of dealers and/or breeders. Nothing new in the fish biz, old as the fishkeeping hobby, in tanks or ponds.
Feed your inexpensive specimens esoteric substances to make them color up and look good for sale. I'm not talkin' color food here. Most common thing would be methyl testosterone. Other hormones also work well to temporarily intensify colors.
Take the fish off the drugs and it fades.
Just a common trick used to justify higher prices for low grade koi.
As for tancho, I tell everybody buying a small one that they are taking a big risk. A good two year old tancho would be the place to begin if you don;t want to lose the spot. Figure a good tancho to cost around a thousand bucks.
Brett