
I doubt if the formula 1/max system resolution = 1/max resolution film + 1/max resolution is correct. In fact, if the resolution degrading effects of the film (various physical effects) are not statistically correlated with the resolution degrading effects of the lens (diffraction and aberrations) then the correct formula is the following (1/max system resolution)^2 = (1/max resolution film)^2 + (1/max resolution)^2. This formula assumes that resolution is defined as the peak width of an image formed by an infinitely small object and that peak width is defined as the standard deviation of the peak, or in other words as the second moment of a peak relative to mean if the peak is normalized to unit probability. This formula assumes linear response, which is not strictly correct for film.
The above description is true, regardless of the shape of the peak. However, if the peak width is defined in some other way rather than the standard deviation of the peak then the above description may either be true or not true, depending on the functional forms of the peaks.
Sorry for all the fancy talk, but I wanted to say it correctly and unambiguously.