example issue date O-A is 13.12.2017. ENTER BEFORE date 13.12.2018. Travel 14.4.2018, than stamp 14.4.2019. Travel again on 12.12.2018, than stamp 12.12.2019. If you travel between 13.12.2018 and 12.12.2019 you need to have a reentry permit.
Thai Immigration has not changed the way of operation, since 2 years a lot of people being denied entry for not having the proper coverage, nothing new. Just get your paperwork in order, I believe the person in question had over 10 years of experience and now he got denied entry.