While there are 5 Seasons in total, Season 0 on YT is referred to as Season 1 on IMDb, Season 1 on YT is referred to as Season 2 on IMDb and vice versa.
There are several episodes that are not included in the official "Episode List" on YouTube. In these, Matt is typically reacting to Reddit posts about the show and looking at fan theories, this therefore means that they would not appear on IMDb either.
The entire video version of the show/series was released on YouTube, where it remains, and therefore means it is not on any other streaming services. After Season 4 (Season 5 on IMDb), the Spellbound team switched over to a paid & written version of the story where it continues, on Substack.
April 25th 2018 was the day the first key, the 863 key was found in the ceiling of Blue Base, starting the entire series.