have pre-1990 stuff in mind (i.e. for the women ranked high on the first list), they may have to reach a bit lower to fill the slots.

I'm hoping it was compiled in the same manner as the Greatest Artists lists and the first Greatest Women list- meaning, VH1 itself did not make it up.
Being VH1, it probably will look a little different than a typical Greatest Women list- i.e. there was a Women Who Rock magazine some years ago, and it had an unranked 100 Essential Women issue and then the 50 Greatest Women issue. Of course, Madonna was No. 1 on the latter- none of the "divas" placed, and were not even featured in the 100 Essential Women issue.