Reported on 1099-b shown basis wasn't reported to IRS

[yj0]

I understand there are cost basis known by broker and reported to IRS and cost basis that are not known to broker and thus not reported to 1099B.

But, what's the point that broker has the cost basis and put it on 1099-B but still wasn't reported to IRS (check box B on 8949) ?     For these transactions, do IRS received the cost basis from broker or not ?

Thank you !

[Bsch4477 · Accepted solution]

The asset was older than time required by the IRS for brokerages to have to give a cost basis. While a cost basis is given the brokerage is not asserting that it is correct. The IRS gets a copy of your 1099-B.