Quick history of Shreddage:
[shreddage -> Shreddage X] -> [Shreddage 2 -> various Shreddage 2.# -> Shreddage 2X]
The samples from the second version of Shreddage (called Shreddage X) were worked into the Shreddage 2X engine, and the package named Shreddage Classic. The "Shreddage Classic Expansion" seems to be the name of this on the website, to differentiate from Shreddage 2 and to emphasize that it's available as an added diversity component (different guitar model, as in the video).
"Shreddage Complete" includes Shreddage (the very first version, ever, with the first scripting engine made for Shreddage in the first place) and Shreddage X (the expansion of the original, that came right after), and the package with both is available under the heading of "Shreddage 1" in the dropdown menu on the website. This is with the old, first scripting engine.
"Shreddage 2" includes, like you said, Shreddage 2(X), Shreddage Classic (Shreddage X implemented into the Shreddage 2X engine), and Shreddage Bass (which has remained as it has always been since its initial release), and is available under the heading of "Shreddage 2" in the dropdown menu on the website. Shreddage 2X, as I've seen it in newsletters, is the naming zircon decided on after several patch updates to Shreddage 2 and the finalization of the skin/wallpaper of the second, new, better scripting engine. This is the newest one, and the package essentially includes all that Shreddage Complete had, but is more uniform with the new engine from Shreddage 2X. You'd get two different guitars and one bass, and one guitar is built for Rhythm and not so much for Lead (Classic), and one is built for Lead but can also do Rhythm very well (2X).