Deductions & credits

Net loss. Bought property for, say, $50,000 in 2005-6?, and had to sell it at a HUGE loss for $4,700 in 2015. Long story, but the facts remain the same. Is it necessary to amend 2015, 2016, and 2017 taxes? Why can I not begin now, filing the property as a loss because I was an idiot then? Something tells me I need that paper trail.