From the way of reading the warscrolls & units sections of the rules, if you use one warscroll, then that is for a unit, and all models of that unit have to stay together. So the only way to have two distinct units of the same type is to have a duplicate warscroll.
It isn't that clear in the rules, but from the description section of some warscrolls you would have to equip everything in a unit with the same thing, and the standard/musician says "Models in this unit may..." Which implies that each unit is one warscroll.
Yes, you literally only need one copy of the printed out physical scroll, as you don't need to waste paper printing it twice. But that's not what they mean when picking number of warscrolls for army selection