So then the difference is between what had been recorded at the time and evidence being discovered and recorded now. I think it all counts as history, whether it be Nostradamus’ Quatraines, cave paintings, distant supernovae or the fossilized remains of some previously undiscovered ancient species.
Counts for what?
If you wish to count everything as "history" and effectively eliminate the concept of "prehistoric", what exactly do you gain?
To repeat: the usual definition of "history" means "recorded history", with "prehistoric" meaning "before recorded history".
I'd say that's still an important distinction, so what is your problem with it?