FWIW
Those
part files are part of what is known as a "spanned archive". Those were originally used to store large files on 1.2M floppies (yes, that long ago

)
Kovid must have done something special, because WinRar can peek, but they do not behave like any typical RAR. With those, launching any of the members, opens 'the parent' (and all the little kiddies)