Your results sound very encouraging! I don't have a densitometer so I cannot measure any densities. Something to put on my list!

Assuming all water was steamed out, the chemicals should increase the volume of solution by about 4 ml/L. So 16 ml of PG yields 20 ml of concentrate. You got 120 ml, and assuming it was hot long enough to steam-out all the water, you must have started with (120/5)-4 = 20 ml of PG. Do you think that's possible?
I made a typo in my posting above, 17ml*5 is 85ml. Anyway, 85ml is the amount of PG I started with. Now, wrt steaming out water, I cannot say. The beaker was heated in a water bath but I doubt I have gotten 20ml extra water from that. I calibrated the pH meter right before measuring but I am starting to question it's accuracy as I leaned a few months ago I had been storing it incorrectly. It's stored properly now, though.

-- Jason