To make sure that you have all of the correct values, yes, you should track down the Form 1099-S. You can confirm that the IRS received a copy of this form by obtaining your 2017 Wage & Income transcript from the IRS (which probably also has all of the information from the original Form 1099-S, but you still want to have the original form for your records):
https://www.irs.gov/individuals/get-transcript
What you need to provide to the IRS to establish the taxable amount, though, are the completed Form 8949 and Schedule D that I mentioned previously.
