2017? Which one?

Hmm, I think he meant the ONA from 2019 (see https://en.wikipedia.org/wiki/Celestial_Method#Anime). Came here to look it up, and couldn't find a way to add a new episode.

Another question: According to this tweet on the 2019 Epsisode, this is episodr 17, with the openeing being episode 14, the ending episode 15 and the OVA episode 16. Should that be implemented and how? Source for this info: https://twitter.com/Infinitedayo/status/1181540810799468545

そらメソの話数表記は制作順番が振られております。１４と１５話はオープニングとエンディング、１６話は特典OVAだったので今回が１７話となります。混乱すると思うので一応説明でした〜　#sorameso

The production order is assigned to the story number notation of Sora Meso. Episodes 14 and 15 were the opening and ending, and episode 16 was a bonus OVA, so this time it will be 17 episodes. I think it will be confusing, so I explained it for the time being ~#sorameso

I think he meant the ONA from 2019

I added the YouTube episode.

Should that be implemented and how?

That would normally be an episode group. But is he counting the opening/ending sequences as two episodes?

As of his tweet (Episodes 14 and 15 were the opening and ending) and the fact that the OVA and ONA are 16 and 17, I guess yes.

You can use an episode group, but the OVA and OVA will have to be 14 and 15. The opening/ending are part of the episodes.