It's in the help but you have to really look for it.

B - incorrect basis on 1099-B

C - collectible

D - accrued market discount

E - sales fees/expenses

L - disallowed losses

N - nominee sales

O - other adjustments and ordinary sale from Section 1242 stock

Q - qualified small business stock

R - deferral of rollover gain

S - ordinary loss from Section 1244 stock

T - incorrect holding period

W - disallowed wash sale loss

X - DC zone or qualified community assets exclusion