The Hohner’s “Meisterklasse” chromatic was introduced around 1982. It was the first high-end harmonica with 14 holes and an anodized aluminum comb. An additional feature were its full-length cover plates, which extend all the way to the ends of the harmonica’s comb rather than sharply angling down before the ends to form an adjoining surface parallel to the reed-plates and comb.
From it’s introduction to circa 1990, Hohner received customer complaints about powdery residue originating from unplated brass reed plates contacting the aluminum comb. The production was stopped. A re-issued version came out about 3 year later (date not confirmed). Additional versions with slight improvements were released thereafter.
I found this interesting website showing a custom Titanium comb for the Hohner Meisterklasse:
An interesting feature is the additional slide button at the lower part, similar to the CBH 2012/2016.
Chromatic Harmonica History 
Thanks for all these articles. I just won this harmonica from eBay. It is with leather box and blue inside. But how do I know if mine is a defect of powdery residue originating from unplated brass reed plates contacting the aluminum comb? Thanks
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What do you mean by blue inside? Do you mean the inside color of the leather box?
Are the reed plates silver plated? If yes, then it is not one of those early ones.
If not and the aluminum is porous (not smooth) it might give you an indicator. I have one of those early MKs. But even that one is still playable. Maybe that hole topic is a little bid overrated. In any case, the chance you got one of those early ones in my opinion is slim.
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