Dont read too much into that word successor (as Chase wants you to do). At most, Chase was successor to servicing, but it was not committed to acquiring all - if any - WaMu notes. There were various limitations on what Chase got from WaMu - substantially all (but not specifically all); and no schedule, no listing, of what, specifically, was to be bought or sold; and whatever anybody thought about buying or selling, it was all subject to approval of all the agencies of the government (which, since FIRREA, gave the FDIC exclusive right of claim on failed bank assets for 6 years - in contract matters, like notes).
And anything Chase would buy, had to be shown in a Receivers Deed and/or a Receivers Bill of Sale - but no such thing was ever written up.
So Chase cannot be said to be any successor to the notes of WaMu.
Selah. (the Biblical Hebrew expression for "Pause, and think about that.)
Now make sure you to that into your case, if your attorney agrees. (I am not one.)