Box 1g. Wash Sale Loss Disallowed
Wash sales. Report wash sale loss amount disallowed. You must report any loss disallowed under section 1091 if both the sale and purchase transactions occur in the same account with respect to covered securities with the same CUSIP number. You are permitted, but are not required, to report in box 1g all loss disallowed under section 1091. For example, you may report a disallowed loss even though a security is sold in one account and repurchased in a different account.
And of course the broker may not have any idea that a wash sale loss was incurred if the purchase of the replacement shares happens in an account at a different financial institution.
