Some time you may need to cut threads on a lathe that are possible, but are not listed in the manufacturer's charts. Or the chart is even wrong! I ran across this with two lathes. The Sherline's optional thread cutting attachment includes a chart that shows most common threads, but certainly not all of the possible ones. The Jet GHB-1340 had several blank spots in the metric portion of the chart (no wonder, they are really unusual values but I hate to see holes in the chart) and some of the values were poorly rounded.
I wrote a couple of Fortran programs that, given the various gear ratios, would calculate all the possible combinations. Note that in some cases the combos may not be physically possible. I did not try them all!
I can't really say how easy it might be to adapt either of these programs to your particular lathe. One key ingredient is knowing your own lathe quite well (what back gears can be installed, what are the ratios provided by the quick-change gearbox).