I did amend the return. The "$90,000 mistake" did not change the tax because the first year depreciation on a $100,000 seven year property placed in service on Feb 1st is $7143.  The actual basis is $10000. On the amended return the actual basis was entered and a $6880 section 179 deduction was taken. That made the first year depreciation of  $264. That made the business profit the same as on original return, so the taxpayers income and thus their tax did not change. On the 1040x all of the original amounts and the corrected amounts were the same. Looking at the 1040x the only way to know that anything was changed is to look at "Explanation of Changes" in part 111 of the form and then look deeper into the return.