Hi Francesca! Welcome to the community!
I second the “curated data cut” as being a good place to start if you’re looking for a combined document. I’d also like to point out that since you’re interested in the prodromal set that there are multiple definitions of prodromal (genetics, hyposmia, RBD, etc.). Not sure which you might be interested in.
For tracking diagnosis over time, I’m going to link to what @jgottesman summarized in another thread - likely you’ll want to track cohort (initial enrollment), primdiag Primary Research Diagnosis, and newclindx Clinical Diagnosis.
For more in depth research, we also have a GitHub repo called PIE-clean that cleans and combines data across modalities, with PIE for more of a machine learning approach to looking at patterns in the data. Lots of work by @cameronreidhamilton and @vcatterson on those two repos if you have any questions.