You may have up to 4 Basic Pokémon cards in your deck with Unown in their names.

This appears in the Unown Pokémon cards of old such as Neo Destiny, even if they have letters like Unown P https://bulbapedia.bulbagarden.net/wiki/Unown_P_(Neo_Destiny_58)) but I have read that 4 of *each* differently lettered Unown is actually allowed? So is this text considered errataed and invalid, right?

More modern Unown P does not have the rules text:

https://bulbapedia.bulbagarden.net/wiki/Unown_P_(Majestic_Dawn_33))

Yes I know the cards aren't currently tournament legal, its for casual play with old cards