I have entered 1098-T information incorrectly for 2013, 2014, 2015 and 2016. Do I need to amend each year, or only the years where the change affected the credit amount?

I have recalculated 2015 and 2016.  2015's credit amount, and therefore refund amount, was affected, but 2016's return was not.  I have not recalculated for 2013 or 2014 yet.

If I file an amended return for Federal, do I automatically have to amend the state (Illinois) for that year?

Thanks.