Facist, are you sure it's not the nature of the beast at hand? Is this any insight as to why two actual 120G SSD's could be listed as 120 or 128G? Once used, wouldn't a 128G SSD with a Marvell controller on an MLC order pretty much instantly become a 120G drive by happen stance? Even if you zero the drive out, once in use a 128G will go right back to 120G.
Of course not a direct answer, but something to research in order to begin forming conclusions for all of us forum readers. 99G free with apps vs 80G free without and I've only assumed 8 of those are theoretically lost. We're looking for 11G that just went into the either it seems; and perhaps more if the second install had no programs (Apps are now for phones) when the first one did.
So feed us please (and I'm not being snarky), why would TRIM and/or ZeroWiping get these holes back on a drive such as this M4?