Hello
Quick feedback on how I solved my problem in the end: the join node proved unreliable (maybe I did not implement it right), some sort of timing or cash issue within the browser, not sure.
Anyways, I eventually used the context approach as described here: A guide to understanding 'Persistent Context'
Everytime a field in my form is altered it stores the new value in a context variable which is saved on disk. At any point in time I can then use context data to compute whatever. Very handy.
