"Necropolis" - changes to creatures of levels 6-7.

That's correct, the manual 3.0 doesn't mention this. But if you look in the editor and copy the data with the descriptions, you'll find all the clarifications clearly laid out in a text file.

As practice shows, you can't fully trust anyone's descriptions. The fact that the coefficient was x2 is confirmed both in the game's internal resources and directly in the game itself (sometimes, even the information in the game's resources may not correspond to reality due to game bugs).