Ed, the C=M=Y applies only to daylight film, assuming equal energy distribution. (Of course sunlight peaks in the green region at about 530 nm (I just have an approximate figure there) and so there is a slight discrepancy in actual practice).
As for Agfa or any other color paper manufacturer, I would assume that either they are correct for their paper, or it is a simplification. To print well from the current population of color negatives, the ordering I described is a virtual requirement in order to avoid color contamination.
The alternative places the yellow layer on top, and adds a yellow filter dye layer, thereby sacrificing dye stability and still begs the issue of printing with tungsten illumination and orange masked negatives. So, in the final analysis, the ordering of color negative paper speeds is C<M<Y to achieve all of the stated goals.
This could concievably be done with a starting filter pack of zero (0,0,0), but then printing would be ever so much more difficult requiring a lot of calulation and zeroing out of neutral densities in the filter packs. So, all manufacturers have apparently done it the way I describe and you can add the goal of simplifying the printing step by only requiring 2 filters (M and Y).