I'm sure you are correct, and I almost certainly used sloppy terminology. I cannot at the moment find the piece that compared it to honey in its "stability." But from wikipedia: "Glycerol possesses the intrinsic property of not denaturing or rendering a botanical's constituents inert (as di-atomic alcohols – i.e. ethanolic (grain) alcohol, methanolic (wood) alcohol, etc., do). Glycerol is a stable preserving agent for botanical extracts that, when utilized in proper concentrations in an extraction solvent base, does not allow inverting or reduction-oxidation of a finished extract's constituents, even over several years."
Also its use as a preserving agent in food and pharma applications tends to argue for its own intrinsic "stability." It is also "bacteriostatic" which means it keeps bacteria from growing...
And you are definitely correct, as well, that there are different grades, plant origins, and even synthetic glycerol (glycerine).
I'll will try to find the honey comparison when I've had more sleep.