Ttax error check implies I don't enter info from 1099B in my return if it "is not reported to the IRS"? This doesn't sound legal tome if I have income!!

the point on some stock sales transactions, is that the stock in question is one that was puchased a long time ago, and that the Broker/Mutual Fund is not required to report the purchase price to the IRS....the broker may not even have the purchase price for those stocks

...BUT...you must provide the purchase price/cost yourself on the stock sales forms for these types of sales.  IF you don't, the IRS will tax you on the entire proceeds of the sale, not just the "gain" .

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At one time...prior to ~5 years ago, the broker never provided the purchase price, but more recent regulations require all brokers to keep track....but just for securities purchased in the past few years.....things bought long ago are considered..."Not Covered", and even if imported form your broker...it may not have the cost listed...so you need to make sure it is in there....or if in there, that it is correct.

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So,,,for all Non covered transactions, you need to edit those stock sales to make sure the proper cost basis has been entered properly.