Asian gold coins weight?

MR168

In JNDA catalog; the 1906 Korean 20 won gold coin weights 16.66g. but two weeks ago in stack's Kroisos sale, one graded Gem BU sold for over 140k weights only 16.49g.
Same for the Chinese 1906 gold coin. In the catalog of Chinese gold & silver coins this coin's weight is 37.15g. But two of this coins both in CU sold in China last year
weight 37.5g & 37.6g. Why there is different in weight? Aren't they suppose weight the same as described in the catalog?

satootoko

Catalogs list the nominal weight specified by a mint. Slight variations are not at all uncommon, and the discrepancies you describe or about 1% are generally within tolerance.

MR168

Thank you for the input, Roy.