Your client’s 1099-B could be long, particularly if they have frequent allocation changes or withdrawals. In particular, if they have enabled TLH+, they may see many transactions. What shows up as a single transaction in their activity tab (Withdrawal, Tax Loss Harvesting) can actually be multiple ETF sales for tax purposes, which is what the 1099-B shows. Sales are grouped by ETF, and within each ETF, by date of sale. They can reference their quarterly statements for a chronological list of transactions, each with a breakdown by ETF sold.
The CSV download of your client’s 1099-B can also be useful to sort the information in different ways, or to import into other software.