With a 1920 POD I'd say that it is a lot more avoidable. At that point you just need one of the two sides to have a more level head for long enough to convince the other side that it isn't worth war. Either Poland needs to offer Germany the access that they want and a promise for a peaceful Danzig resolution, or Germany needs to renounce some of their claims and maybe offer to help back Poland's claim on Vilnius/Wilna in exchange for Poland helping them get back Memel.How inevitable with a 1920 POD then would you say was a Polish-German War sooner or later, with the mess of the Polish Corridor that you noted and all that.
In my opinion, when it comes to claims on Poland, it isn't so much one big issue of claims; rather, 3 separate claims which have to be handled uniquely, those being Posen, Upper Silesia, and West Prussia. Everyone agrees that the West Prussian claim is the most legitimate and the easiest to gain sympathy on. Upper Silesia is harder since it is a huge part of Polish industry, but there was a lot of interference in the election there and Germany could press that fact. Then there is Posen, where Germany's claim is weakest since the region revolted against their control, but which they nevertheless view as an integral part, even if only because of how the infrastructure there makes it into one solid unit connecting Prussia to Silesia.