Either way, a gallon of this stuff would last even the heaviest vaper for a several years at least. Just did some calculations for 16mg NIC after cutting from 48... to use the whole gallon of PG would need 1890mL of nic pg!
That's what I thought, too, but it turns out that I use pg for more than just making juice.
I do a lot of flavor testing. This only uses a bit less that 1ml per test, but I do several tests/day, usually, and they add up fast!
However, my biggest use (outside of actually making juice) is in rinsing. I drip into a debridged/dewicked atty for testing and test several flavors at a sitting. In between flavors, I blow the atty out, then put about a ml of pure pg into it, blow it out again and repeat. Some flavors need more than two such flushes, but this quickly clears the old flavor out so I can taste the next one cleanly.
Looking at how quickly I'm draining my current gallon, I think I will end up going through a gallon in 3 or 4 months.