Henry,
You are so right. There are so many opportunities during the life of a koi for infection and injuries to ocurr . When you see a large specimen of ANY variety that is an almost perfect example of that variety, it is a great testament to the person who has kept that koi to get it to that size and age in that condition.
It has not been until the last year or so that I have begun to understand how judges can be so 'forgiving' of flaws in a large koi when it is being judged against a smaller, younger koi of the same variety that may have more intense color or a better pattern, but falls short in conformation and the presence that a larger koi carries with it.
I have an asagi that lost a scale 3 years ago. It has never regrown. There is a white spot in the net pattern where the scale is missing. This spring my female gin rin kohaku was banged up by the males in my pond. The kohaku lost two scales in the hi pattern.
Just this week I snapped several pictures of my fish and happened to get these two fish in the same picture. Have a look and you will see the two missing scales on the kohaku directly above the back of the pectoral fin on the side of the fish. The missing scale on the asagi is in about the same position. I'll post an overhead view of the asagi in which the missing scale is hardly noticable.
Good luck with your kohaku. I will keep my fingers crossed for both of our kohaku hoping both regrow the scales. Brady Brandwood visited here in late May when this kohaku still had pink bruising showing in the shiro areas. He gave the fish a good look-over and said he felt there was a good chance the two scales would grow back and fill the pattern. Of course, it may not, if it goes the way of the asagi.
Dale