Github user aljoscha commented on the issue:
https://github.com/apache/flink/pull/4665
@Aitozi I meant that the place where you're currently counting dropped
elements will not yield a correct count because one element might be in several
windows. The place were we side-output late data is also the place to count and
here we can decide if we want to count late data as dropped if we also
side-output it. I think it's a question of personal preference.---
