They've also forgotten the bulkhead in the butler's pantry and that's definitely in the drawings as well. Having things written up or drawn up in the contract/plans/etc does not necessarily mean they won't miss a thing. You just have to be vigilant.
Wow, that's so annoying. At least you have it in the contracts! It definitely clears it up that it's their fault and gives you leverage. What are your options now? Are they going to refund you the forgotten bulkheads or are they going to have to install bulkheads even if they have to pull out the already installed overhead cupboards etc