I did a quick test, if anyone could confirm the result, that would be good.
Using "tes3cmd diff" I did a difference report for MCAFix.esp and MCA.esm. This shows that 10 lists are exact duplicates, and 2 lists are changed in MCAFix.esp: _mca_ex_bandits_towns and _mca_ex_other. We can ignore the dups, I think.
Then I generated a new Mashed Lists.esp while MCAFix.esp was in my load list. In the resulting Mashed Lists.esp the two lists (_mca_ex_bandits_towns and _mca_ex_other) are the same as in the original values of MCA.esm.
If I've made a mistake, please let me know.