You've mentioned LT Capital Loss, Form 4797, Involuntary Conversion, and Ponzi Scheme.  What EXACTLY happened?

IF this loss was properly reported on Form 4797, that loss should have been FULLY allowed in 2016, and there is nothing directly carried over.  It would have offset any other income on the 2016 tax return.  If there was no income on the 2016 tax return, then that loss would have created a Net Operating Loss.  If the election to 'waive carryback' was not made, the NOL would be first carried to 2014, then to 2015, 2017 and then 2018.