The News / splash adverts on the launcher have to link to an underlying blog post. So, if there was a Season 17 ending splash, there had to be a corresponding blog article for the splash to point to.
I had a look at…
https://news.blizzard.com/en-us/diablo3
…and there’s no such article.
Well it provides you the info now, it didn’t when I did the search earlier this month. 
In the end it’s all pixels so it doesn’t really matter, but when it comes to good communications I always hope in time it gets better in all areas of life, after all we are supposed to progress as a species both ingame and irl!