Most recent use of each letter noted.
A
April 2020, Sept. 2020, Nov. 2020, Dec. 2020, Jan. 2021, Feb. 2021, June 2021
B
Aug. 2020, Oct. 2020, Nov. 2020, Jan. 2021, April 2021, May 2021, July 2021
C
Aug. 2020, Oct. 2020, Nov. 2020, Jan. 2021, Feb. 2021, April 2021, July 2021
D
May 2020, Sept. 2020, Nov. 2020, Feb. 2021, March 2021, June 2021
E
July 2020, Oct. 2020, Dec. 2020, March 2021 (twice), June 2021
F
April 2020, Sept. 2020, Dec. 2020, Feb. 2021, May 2021, Aug. 2021
G
Aug. 2020, Oct. 2020, Nov. 2020, Jan. 2021 (twice), May 2021
H
May 2020, Sept. 2020, Oct. 2020, Feb. 2021, April 2021, June 2021
I
July 2020, Dec. 2020, April 2021, May 2021
J
Jan. 2020, Aug. 2020, Oct. 2020, Jan. 2021, June 2021
K
July 2020, Nov. 2020, Feb. 2021, April 2021, June 2021
L
June 2020, Oct. 2020 (twice), Dec. 2020, April 2021, June 2021
M
Aug. 2020, Nov. 2020, Jan. 2021, April 2021, May 2021
N
May 2020, Sept. 2020, Dec. 2020, March 2021, June 2021
O
June 2020, Oct. 2020, Dec. 2020, April 2021, July 2021
P
Aug. 2020, Oct. 2020, Jan. 2021, Feb. 2021, May 2021
Q
June 2020, Oct. 2020, April 2021, July 2021
R
Jan. 2020, Sept. 2020, Nov. 2020, Jan. 2021 (twice), May 2021, June 2021
S
July 2020, Sept. 2020, Oct. 2020 (twice), Nov. 2020, Jan. 2021, May 2021
T
Aug. 2020, Nov. 2020, Dec. 2020, Jan. 2021, May 2021, July 2021
U
Feb. 2020, Nov. 2020, March 2021, June 2021
V
Feb. 2020, Aug. 2020, Dec. 2020, March 2021, July 2021
W
March 2020, Sept. 2020, Dec. 2020, March 2021, May 2021
X
July 2020, June 2021
Y
April 2020, Aug. 2020, March 2021, June 2021
Z
May 2020, Oct. 2020, Jan. 2021, March 2021, July 2021
(As of August 2021 thread, post 1)