Difference between Tender Drawings & Contract Drawings

Dear Members,

Sorry for a long delay with this form.

I Have a topic regarding the the subject issue...

My contractor is bound in Lumsum Contract.He was the ( Nominateded Person signed Condition of Acceptence showing date );Now the Contractor is furnishing a claim interpretating the difference between the subject item..!!!

As a Consultant I just object this claim in accodance with the signed Letter of Acceptance with date ..?

Or shall I specifically check the Agreement date to counter argue with the Contractor....?

Please ,experts just clarify...!!!!