Exactly. I think everyone is perhaps placing too much importance on whose lightsaber is whose.
For one, the one on the far left looks like nothing in game or previous trailers.
Also, Darach and Zallow both used the exact same lightsaber, as did every, single Jedi in the Deceived trailer.
"Malgus' saber" is not "Malgus' saber" at all. Just a generic model used in game. The one he had in the previous trailers (Hope, Deceived) look nothing like that.
And finally, the one you are saying is Vindican's is single bladed saber, he used a double. Yeah, maybe Malgus cut it in half and rebuilt the pommel to turn it into a single bladed lightsaber? But, why would he?
And come to think of it, the same thing was always true for "Revan's" saber in game. It's just a generic model that many NPC's used. it's not really "Revan's saber" when dozens of other NPC's and players can get the same model. Bioware dosen't place any importance on "this item is this character's and only this character's". All just generic reusable items. Sorry to burst all those bubbles.