For collectors the changeover is a complete mess. One country makes changes to the obverse, some make changes to the reverse but most countries have as yet not made any changes at all. I have the following information on recent changes apparently made to reduce the loss on the production of the euro coins:
Ammended reverse:
Italy 2017: 1 and 2 euro cent
Austria 2017: 2 euro cent (issued with both old and new reverse)
Austria 2018: 2 euro cent
Ammended obverse:
Germany 2 euro cents:
2016: G
2017: A, G, J
2018: D, F, J
Let's see if we can find some further ones.