Most recent use of each letter noted.
A
April 2020, Sept. 2020, Nov. 2020, Dec. 2020, Jan. 2021, Feb. 2021
B
Aug. 2020, Oct. 2020, Nov. 2020, Jan. 2021
C
Aug. 2020, Oct. 2020, Nov. 2020, Jan. 2021, Feb. 2021
D
May 2020, Sept. 2020, Nov. 2020, Feb. 2021
E
July 2020, Oct. 2020, Dec. 2020, March 2021
F
April 2020, Sept. 2020, Dec. 2020, Feb. 2021
G
Aug. 2020, Oct. 2020, Nov. 2020, Jan. 2021 (twice)
H
May 2020, Sept. 2020, Oct. 2020, Feb. 2021
I
July 2020, Dec. 2020
J
Jan. 2020, Aug. 2020, Oct. 2020, Jan. 2021
K
July 2020, Nov. 2020, Feb. 2021
L
June 2020, Oct. 2020 (twice), Dec. 2020
M
Aug. 2020, Nov. 2020, Jan. 2021
N
May 2020, Sept. 2020, Dec. 2020
O
June 2020, Oct. 2020, Dec. 2020
P
Aug. 2020, Oct. 2020, Jan. 2021, Feb. 2021
Q
June 2020, Oct. 2020
R
Jan. 2020, Sept. 2020, Nov. 2020, Jan. 2021 (twice)
S
July 2020, Sept. 2020, Oct. 2020 (twice), Nov. 2020, Jan. 2021
T
Aug. 2020, Nov. 2020, Dec. 2020, Jan. 2021
U
Feb. 2020, Nov. 2020
V
Feb. 2020, Aug. 2020, Dec. 2020
W
March 2020, Sept. 2020, Dec. 2020
X
July 2020
Y
April 2020, Aug. 2020, March 2021
Z
May 2020, Oct. 2020, Jan. 2021, March 2021
(As of March 2021 thread, post 69)