Very helpful. My point was that I get sometimes both--I've had some rolls that I slightly underexposed with cyan and other rolls with magenta, and as far as I could tell, no rhyme or reason.
I began to overexpose by 1/2 stop and found that they looked perfect.
It is probably from shooting in color temps other than 5,500K, or whatever the film is balanced for. The extra exposure you gave the film likely made accurate color correction possible by giving all the color layers adequate exposure.
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