On sudopedia I found the two (of six) elimination rules for 3D medusa coloring.

# 2 colors for one digit appear in a house with more than 2 candidates for that digit. The uncolored candidates can be eliminated.

# An uncolored candidate X can see two differently colored X in two different houses. The uncolored candidate can be eliminated

This sounds to me like a single rule, which is unnecessarily split up in two rules,

dependent on in how many houses the two candidates of the same digit

but distinct parities appear, seen by the CEC.

I found it confusing, that scanraid uses the same separation in two distinct rules.

On 9981, the second rule is not documented.

If 9981 is a copy of an earlier version of sudopedia, then the second rule was maybe added later in sudope.

I think it would make sense to rephrase the first rule and skip the second.