CecilOne wrote
Also, a play at the plate overrides PU coverage of 3rd.
Perhaps this is also the reason why baseball plate umpires do not rotate to 3rd with runners in scoring position, except on the R1/R2 situation, fly ball to the outfield <2 outs, and R2 tagging up to go to 3rd (R1/R3 is a rotation situation in 2-man (and some 3-man systems) and R3 is also a rotation situation in softball (and some baseball) 3-man on batted balls to the outfield, but those situations are exceptions, because the runner on 3rd base is expected to score without a play made on him/her).
In softball 3-man, none of the OP situations involve rotations, because umpires would be in the counter-rotated position (U3 is in D, U1 is in B).