I am not sure, but I think in 7th edition, you could have more than two by capturing standards, hence the point of the Cursed Banner. I think it's been a while for @Eternal Salvation, so he might need some brushing up on rules changes.
"Capturing" a banner doesn't do anything in 8th edition except for Beastmen and Blood and Glory, I think. Even then, Blood and Glory doesn't really count it as "capturing," you just have to kill the bannerman. I didn't play 7th edition much, but I know that the cursed banner, when captured, caused D6 S4 hits against the unit; the unit could discard the banner to stop taking the hits, but would lose the capturing bonus. I don't know if capturing a banner otherwise did anything for the unit. Regardless, two is the max for 8th edition.