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taxes, ordinary income, and adjusted cost basis for RSUs
What happened is that they do not track (and report) your original cost basis for 1099-B purposes. That is because it is an RSU. Instead, they just reported gross proceeds ($5200) and $0 for everything else. On your Schedule D you adjust the basis to the correct one, and as a comment you add that it was reported on W2 of the previous year. You then report the correct $1200 gain. You keep the documentation you have to back this up in case of questions (which shouldn't happen, since it will match what was indeed reported on your W2).