Take a good look at the tax bill for 2016 they sent you.
Also get a transcript from IRS for 2016. https://www.irs.gov/individuals/get-transcript
The reason for this is when IRS sees stock sales NOT reported they many times give you a $0 cost basis and tax it at Short-term gain, when you have a cost basis and it should be long-term.
So YES, if that is the case I would Amend and the tax on the return is actually what is assessed on the tax transcript by IRS.
Yes, you make perfect sense, and this Amended return could save you a lot of money.
