Things like this are why I stick to 5ABY onward.
Ah, an EU fan, I see. Yeah, I've mostly stuck to the books, haven't really gotten into any Prequel EU (unless it was fringe stuff, like
Coruscant Nights). Even what I've read was already screwed over by TCW. Even Piell was killed off in TCW prior to his already-established death in
Coruscant Nights. And Leland Chee had absolutely no retcon to explain that away and backpedaled so fast that he left a rut.
Then, there was Greedo appearing in
Sphere of Influence, which took a big, steaming [parasitic bomb] on
A Hunter's Fate. Now, Dengar, complete with headdress (apparently some cultural thing), appearing in TCW. Bossk was bad enough, but his appearance could be forgiven as Bossk is long-lived and has been around that long.
Everything that hasn't been screwed over yet is still ripe for the picking in Filoni's canon-sodomizing siege.