Omission sometimes could be a serious problem in quantity survey, how do you resolve this issue, especially when a bill has been forwarded?

Omission and Addition of quantities or scope of works in a BOQ of a Remeasureble form of contract is not a problem .It could be done by both parties Contractor & Owner. For contractor they could submit Technical Queries or Request for Variation Order to the Client. In the same way client  could issue a notice to the contractor for omission or addition in a form of Variation or Changre Order.

However in a government project specially here in KSA Change order must not exceed20% from the total Contract Value and proper documentation is very important in this issue.