Howdy,
Did NGC ever conclude this question? Looking at one of the type scores for Morgan and Peace dollars in one of the 20th Century Type Sets (https://www.ngccoin.com/registry/competitive/united-states/type-sets/215/definition/#8761) it lists "2021 Morgan $1 Advance Releases MS " as eligible for the Low Relief Peace dollar slot, which is obviously wrong since 2021 is not in the 20th Century, and a Morgan $1 is not a Peace $1, but it made me wonder if this issue was decided.
For some reason, there are a bunch more "not eligible" coins listed as "eligible" in the the Morgan and Peace dollar slots for 20th Century Type Sets, e.g. (1526-7) ITALY FLORIN FLORENCE FR-276 FRANCESCO MARTELLI MS , (1565-1602) INDIA PAGODA NAYAKAS OF CHITRADURGA MADAKERI NAYAKA - GOLD MS , 1549 FRANCE CAROLU BESANCON MS , AH1255//12 TURKEY S20P MS , and a bunch more.
Thanks