When Sec. 121 was created (1997?), the INSTRUCTIONS to Sch D stated that if your gain was below the maximums you were not required to report the sale.

Since the IRS does not know the cost or adjusted basis, you would be foolish to fail to report it if the sales was for more than 250/500, regardless of gain.

Sales price 250/500 or less? You cannot have a taxable gain. More than? Without proof? How to prove it's not taxable unless you report it.