Hi. I’m an old-time UK comics collector, and have owned several copies of the above-mentioned hard cover annuals.
Unfortunately I no longer own them, so I can’t offer 100% proof, but I believe there are 12 different annuals in total. They are: the nine that are pictured above, plus Doom Patrol, Mystery In Space and Wonder Woman. I have owned (or seen) the Mystery In Space and Wonder Woman, so I am 100% sure they exist. I am only 99% (!) sure about the Doom Patrol one, but am pretty sure I have seen the cover printed somewhere.
They are indeed all quite scarce. My experience suggests the Showcase one is the commonest and the Doom Patrol is the rarest, but that’s just anecdotal.
A friend of mine owns most of them, and I have told him about this thread so perhaps he will post and give you more information.