JCT D&B 2016 with BoQ - Quantities change risk on time

Working under a JCT where the quantities on the BoQ is different than those shown on drawings. If the quantities later change - who holds the risk on time - specifically if the quantities increase?

Particularly relevant in tendering, do you price the bill (technically yes), but programme the drawings? Assuming any deviation on drawings (revised drawings issued) would be deemed a relevant event/ matter and deal with change that way?