When did they change the derby cover size?

I bought a new 2016 FLTRU and noticed that the derby cover is about 1/2" larger in diameter than my 2013 FLTRU. Does anyone know when they changed? I'm thinking maybe 2015 when the Rushmore changes were made but I don't know for sure. I have a custom derby cover off of my 2013 (originally on my 2005 FLTRI)that no longer fits on my 2016 and would like to give it to one of my friends but I'd like to know for sure what years it will fit.