I cannot find the due date for filing a carryback claim for 2014 for a loss created by the amendment of a 2016 Form 540. And in case it makes a difference, the 2016 Form 540 was amended to claim a casualty loss experienced in 2017 in a federally declared disaster (CA wildfire).
Under normal circumstances, the 2014 return must be filed within 4 years of the filing of the original return. If, however, there is an NOL, you should file the 2014 year when filing the amended 2016 which would have a 4 year statute, so 2020. If it was a disaster in 2017 the return was due in 2017 to elect to claim on 2018.