I think best is to skip the sub-releases, as 184.108.40.206 is 18c and 220.127.116.11 is 19c - MY personal upgrade from 12c OCP should/would be 20c, I think... also with former releases one is able to skip a version and take a "double upgrade" exam. Also there are not that much new features in 18.104.22.168/18c which would make a need to have a 18c OCP exam.
And last, but not least - I like to learn with some preparation books, but you can't find some for 12.2 and 18c.
I am try to learn a little bit for a Cloud certification, but it is really not easy just using elearning material...
We don't really have an answer to this question yet. This is all still being worked out - as far as what will be required and when. We will publish all details on the Oracle Certification Blog when we have a change in requirements.
Thanks for posting!
Oracle Certification Program