If the CWIs were working for you, didn't you check their reports before submitting them to the customer? If they were doing a poor job, i.e., not providing the information required, why did you let them continue?

Now that the job is completed, how do you go back and determine which welder made each weld? Were the welders required to stamp their welds or was a weld map maintained? Were your welding inspectors serving in the roll as the contractor's inspectors or as verification inspectors? Was it a contractual requirement that the contractor keep track of which welder made each weld or was that requirement imposed on the verification inspector?

Just asking the hard questions friend.

Unfortunately, unless there is a way to determine who welded what, you may end up eating the bullet on this one if the CWIs were employees. If they were independent contractors, what did you provide them in writing? Were they provided with project specifications, drawings, purchase orders, contracts? Without the necessary documentation they may be considered employees in which case they will be entitled to additional wages based on the number of hours required to untangle the worms.

Best regard - Al