That I wouldn't know, becasue they don't reveal anything (unfortunately) about their extracting process. But, I can tell you out of all the blends I've tried from HHV, the recommended 70pg/30vg is the best flavor. I am one of those all vg guys and I love it when I can get it, but it was not the same with HHV. It's odd because some of the all vg blends I've had were producing crazy flavor and vapor, but as Adam said, most of those all vg juices haven't been tasted any other way. That is true. Most of my beloved vg juices have only ever come in all vg so I cannot say how they taste in a different mix. If you try HHV's Putirty in 70pg/30vg you probably will be dissapointed in anything else...HHV's delightful notes must be heard and I don't think the other heavier vg mixes are sensitive to picking up those frequencies.
An interesting side note: HHV's all vg is not thick at all. I seem to get better performance out of less thinned vg, so if you are looking for a thick vg, you may have to consult with Adam and Heather. However, if you are an all vg vaper due to allergies, then by all means have at the all vg, for if you only will have tasted it in one way, you will know know difference.