(1)Reading the thread Choice benefit Did I miss email , would DL have sent me an email reminding me that I haven't made my selection?
(2)I left AA in early Jan. 2019 and did a DL accelerated PLAT "challenge" and succeeded, since then I've flown enough to be PLAT and by year end should be DIAMOND.
(3)Now I have choice benefits available for 2020 and 2021, why both?
(4)When I become DIAMOND do I still keep my choice PLAT benefits?
(5)How are RUCs prioritized? If I try to use one and it doesn't clear is it lost forever?
The status you earn this year is for next years status. (DL allows to use the status right away, nowaiting) The dates you list are when the elite year ends. For 2019, that's Jan 31, 2020. For 2020 elite year that is Jan 31, 2021.
Yes you keep PM choice when earning Diamond. They're wholly separate.
Certain benefits have different expiration dates. GUC/RUC expire one year from selection date. Thus don't select till ready to use. Skyclub membership goes through end of elite year. (I used a 2020 selection for SC and thus have membership through Jan 31, 2021)