Great question, I would like to know also,hope someone chimes in?

Breeders use the word stable not as a discrete term, but in context. For example, I might say, "ISS is stable for smell, taste and high profile, but variable for most other traits." Some 'strains' have very little variability of any kind, but these are usually the product of backcrossing, which although it does reduce variation, doesn't guarantee plants that have the target traits. What kind of stability you can expect depends entirely on what was done to the strain before you grew it. If it's the product of recent outcrossing, you can't expect much stability of any kind. If it's been inbred (brother to sister) for 6-7 generations you can at least expect stability for the targeted traits. True IBL's are as rare as hen's teeth in the modern cannabis breeding scene. 'Cubed' or backcrossed seeds are far more common.