Hi,
Theoretically, depending on precision required, the datasheet should suffice for lowest and highest points to find the best fit - accepting a certain % tolerance/variable will be there in reality beyond calculations. I think some circuits do need the device to be tested first otherwise the results are way off. Different but similar, NFETs I have have a wide ranging VGSoff, designing a reasonably precise circuit is not possible with even a variable VGSoff in the same pack of NFETs that so far have ranged from -1.8V to -2.8VGSoff (grrrr).