Here's a link
to a cached version of that article, for any who might be suspicious of a Tumblr repost.
I was hoping they'd be announcing more, both because I hope more exists and because rumors will swirl that there's more anyway. But others can worry about that. Nine episodes, four from one of the most-desired stories, is extraordinary enough.
Nigeria again-- I think that was also the source of the largest previous return (barring what the BFI sent back), when a bunch of episodes came back in the mid-1980s.