Well oddly enough there is more from ANH in private collections than most of the films as there was essentially no security.They just didnt think it would be that important to keep it or that they would need any of it again.Costumes,helmets,lightsabers all chucked in a bin out the back of Elstree or taken home by the crew.To my understanding this jacket was sold in the US and has very solid provenance.Actually on this topic a friend of mine recently bought the trousers worn by Cushing as Tarkin in ANH.Prices now are much,much higher as the profile of the original prop hobby has been raised and it is now known how much money is to be made from it but years ago it wasn't as widely recognised and things went pretty cheap.
Lucas didn't actively start building the archive and putting all the stuff in it until ROTJ so there is actually comparatively little in the LFL archive from ANH and ESB.