You did *not* receive distributions of the excess contributions before the dues dates of your 2016 and 2017 tax returns, respectively. Because these excess contributions were not corrected before the end of 2018, you owe the same penalty for 2018 as you owe for 2017. Excess contributions corrected after the due date of your tax return are only corrected for the tax year in which the distribution of the excess occurs and subsequent years.
I've added to my answer describing how these excess contributions should have been corrected in 2019.
