Why do some capital gain/loss show up on Schedule D line 8a vs 8b

Essentially line 8a reports any 1099-B transactions that are not included on the 8949 on line 8b.  In some cases, all transactions can be included on the 8949 line 8b.

Lines 1a and 8a— Transactions Not Reported on Form 8949

You can report on line 1a (for short-term transactions) or line 8a (for long-term transactions) the aggregate totals from any transactions (except sales of collectibles) for which:

• You received a Form 1099-B (or substitute statement) that shows basis was reported to the IRS and doesn't show any adjustments in box 1f or 1g;
• The Ordinary box in box 2 isn’t checked;
• The QOF box in box 3 isn’t checked;
• You aren’t electing to defer income due to an investment in a QOF and aren’t terminating deferral from an investment in a QOF; and
• You don't need to make any adjustments to the basis or type of gain or loss reported on Form 1099-B (or substitute statement), or to your gain or loss.

See How To Complete Form 8949, Columns (f) and (g) in the Form 8949 instructions for details about possible adjustments to your gain or loss.

If you choose to report these transactions on lines 1a and 8a, don't report them on Form 8949. You don't need to attach a statement to explain the entries on lines 1a and 8a and, if you e-file your return, you don't need to file Form 8453.

Figure gain or loss on each line. Subtract the cost or other basis in column (e) from the proceeds (sales price) in column (d). Enter the gain or loss in column (h). Enter negative amounts in parentheses.

Lines 1b, 2, 3, 8b, 9, and 10, Column (h)—Transactions Reported on Form 8949

Figure gain or loss on each line. First, subtract the cost or other basis in column (e) from the proceeds (sales price) in column (d). Then combine the result with any adjustments in column (g). Enter the gain or loss in column (h). Enter negative amounts in parentheses.

Please see the IRS publication: Instructions for 2022 Schedule D

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