Curious NGC Variety Attribution Change

I have noticed that NGC has seemingly changed is variety attribution for the South Korean 10 Won coin from this:


Here, NGC are clearly attributing this 10 Won coin as the "Bronze" variety. Prior to July 16, 1970, the Korean Mint struck these coins on 88% Copper, 12% Zinc planchets. After this date, the Mint changed the coining metal for the 10 Won coin to 65% Copper, 35% Zinc planchets. This created two varieties for 10 Won coins dated 1970. Although both metals are actually brass, Korean collectors began calling these the "bronze" variety (the former) and the "brass" variety (the latter). The Krause SCWC gives these coins a separate identifier: KM-6 (for the bronze), and KM-6A (for the brass).

Now, it seems as if NGC isn't making a variety distinction. Look at this:

It doesn't look like they attribute the variety anymore. I also see that there isn't a KM number cited, either. Perhaps they have conceded to the reality that you really cannot tell the difference between a coin composed of one percentage of copper/zinc over the other. Some say that there is a color tone difference. But how can you really tell? The only way might be a very sensitive, laboratory-controlled specific gravity test.

Does anyone here know what this is all about?