Several of RG's balls have an asymmetric core and are not marked. Mostly it's because theasymmetry is slight and the mass bias strength is low. I believe the cutoff point is approximately .008 mass bias differential. Below that the mass bias is not strong enough to make a difference - thus sayeth Mo Pinel (and several others).

Neither of MoRich's first 2 balls, the Labyrinth and the Minotaur had a strong enough bias for even Mo to list it on their webpages. Their first ball with significant Mass Bias was the Colossus at .009.

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Bowling: Just like hand grenades and horse shoes, you only have to get close.
Life: Deal with what is.