The basic references are included in the web form and on the header of the output file.
CMD is being extended/updated every few months. The latest version is always linked in http://stev.oapd.inaf.it/cmd. Older versions are stored in pages named http://stev.oapd.inaf.it/cmd_N.N, where N.N is the version number. The oldest versions are outdated, and may not work.
When options 2 or 3 are used, most stars with small luminosity/mass ratio are assigned a value pmode=4. This does not necessarily mean that the 4th overtone is really dominant. Indeed, there seems to be no clear observational detection of the 4th overtone mode in AGB stars, suggesting that it either is stable or has very small amplitude (see Trabucchi+2017). Therefore it is reasonable to interpret the occurrences of pmode=4 as an indication that the star displays only small-amplitude oscillations, if any. The origin of this patter is the following. The prescription from Trabucchi+2019 used to assign the value of pmode exploits the fact that the dominant mode shifts towards pulsation modes of increasingly smaller radial order as the stellar luminosity increase. This is achieved by comparing the actual luminosity of a simulated star with the value of luminosity corresponding to the transition between two pulsation modes. Since the pulsation models of Trabucchi+2019 do not include properties of pulsation modes higher than the 4th overtone, there is no prediction for the lower luminosity boundary of the regime in which it is dominant.