This note is from the DE book & Errata, but I'm pretty sure is in all of them:
Page 100 – Common Magic Items.
Note that if a Magic Item is listed in both an army book and
the Warhammer rulebook, use the points value given in the
Army Book, with the rule printed in the Warhammer rulebook.
So in the BRB, War banner is 35 points, but the army book is 25.
A couple other items are cheaper, most are the same.
The only one I have that's more expensive is Enchanted shield in the BRB is 5 points, 15 in the army book.
So if you've ever used that shield as a 5 point filler, you may have gone over the limit.