Speaking of the 200th Yahrzeit of Rabbeinu, as the letter Reish=200, the first letter of the word Rabbeinu, as well as the letter of the highest Gematria value in the word, the letter Reish is the 20th letter of the Alef Beis. Accordingly, the word for 20 is Esrim, the word itself being the Gematria of 620. The word Keser, the highest of the Sephiros, is also the Gematria of 620.
Rabbi Moshe Cordovero (whose Yahrzeit of 23 Tamuz is the same date on which Saba discovered the Petek) states that the Aseres Yemei Teshuva correspond to the 10 Sephiros from the highest to the lowest - Keser, Chochma, Bina, Chesed, Gevura, Tiferes, Netzach, Hod, Yesod, Malchus. Thus, Keser corresponds to the 1st day of the Aseres Yemei Teshuva - (the first day of) Rosh Hashanah, about which Rabbeinu said that this is his whole essence. Moreover, the very beginning of the Mishna tractate Rosh Hashanah mentions the date of Rabbeinu's birth - Rosh Chodesh Nissan.