Do they all contain separate assets? But if this is the case, then,  where are one and two? 

And if they are updated versions of the older packs, then why is the 3rd one bigger than all the rest of them?

I keep the older ones up for a bit, but the latest asset has the most recent changes. I am not sure why the 3rd is bigger, I think I had removed some assets at some point. The changelog goes through the details :)