BioGeoBEARS is a fairly large package and it's just little-ol'-me programming it in between all of the other stuff I have to do. In some cases I will have added features to some functions, that have not been fully integrated throughout the package. YMMV (your mileage may vary) with those options, or they may just result in errors.
I'll list them as I remember them. I may also list here features that people ask for, but that don't currently exist.
By default, include_null_range=TRUE, and this is assumed by all functions. The null range is a state where a taxon lives in no areas. Setting include_null_range=FALSE removes this state from the state space, and requires other adjustments throughout the code as the null state has to be treated specially in the calculations (it is impossible as an ancestor, for instance).
Short version: include_null_range=FALSE will work in simple functions like numstates_from_numareas, but not complex ones doing ML searches and ancestral state estimation.