JCT: Contradictory provisions

On a JCT Sub-Contract (JCT DBSub), where the re-measurement basis applies, clause 2.9 suggests that an error in quantity is to be corrected and treated as a variation whereas clause 5.1 says that a change in quantity is not a variation. Are these clauses therefore contradictory (or is the correct interpretation that errors in the BoQ quantity (e.g. a BoQ quantity which differs from a contract drawing quantity) are corrected and treated as a variation whereas other changes in quantity where there is no error (for example arising from a design change) are not a variation)? Given that the entire works are to be remeasured here, does clause 2.9 have any real relevance on a JCT remeasurement sub- contract?

The latter interpretation is the correct one, it’s not intended that departures, errors, and omissions in the BoQ are the Contractor’s risk. The term “treated as a Variation” effectively means the definition of the term Variation at clause 5.1 is extended to include this risk.

Clauses 2.9 and 5.1 deal with different risks and the Valuation of variations in each instance is different.