And it's worth noting that the 5329 amounts do snowball.  So an excess contribution in 2015 is still an excess contribution in 2016 (part IV line 18), add the 2016 amount, then the 2016 total carries to 2017, add the 2017, carry to 2018 and so on.

I haven't done the research but I've heard that 5329s have their own statute of limitations.  So if one was never filed in the earlier years, the clock never starts running.  I've seen some CPE folks recommend that you file a $0 form every year just in case something like this comes up.  I filed that information in my brain under "things I heard that I don't necessarily believe" but I've never had one go more than three years back so I've never had to research it.

Rick