You get everything from donators.

The video release flow is: Donators -> Admirer -> Contributors -> Writers" That means, as a Contributor, you have all the videos from the Donators and Admirers tier as well. All the series are not exclusive to tiers and some episode may be on different tiers. So if you want to have everything 100% need the Writers tier

Also you get access to the fan fiction forum(read only) and post on the nsfw discord channel