I DIY using both PG and VG. I also use premixed flavored juices. I wish I knew the answer to the differences in the same grade PG and VG. There are definite differences. IE: I
vape a 50/50 from one vendor and a 67/33 from another. There is much, much, more vapor (same setup) with the 67/33 than the 50/50 which makes no
sense other than a difference in the brand of bases. Unfortunately, the vendor selling 67/33 premix charges $8.00 for 36mls of both plain PG and VG which is about half the price of a premix with nic and flavor. It sucks but I continue to
buy it as I get the best results with them. (His premixed is priced very competitively but not the plain PG/VG.) This vendor knows there are differences in these two bases or he wouldn't sell the plain at such a high price. I, for one, have found it to be worth it. I continue the search though and the PG I get from One Stop DIY is the next best IMO but can't say the same for their VG. I've tried the Walmart VG even and... forget it... that stuff is awful.