JCT (ICD) 2016 Inconsistency of documents - Rectification Period

Under the JCT contract, during the tender period, I submitted a set of preliminaries to the tenderers. After the contract award, I provided the contractor with the contract documents to sign and return for execution as a deed. During this process, the contractor noted that in the preliminary document under Rectification Period (clause 2.30), no period was stated, so technically the period defaults to six months. On the contract documents, I stated the period as twelve months. The contractor is now charging us £950 to revert it to 12 months. Is this the right procedure to take, and which document takes precedence? The contract does not spell out what to do in this situation.