I agree, reconcile to the VAL.
Depending on the version and history of the Sage100 / MAS system.. the TB vs VAL vs Stock Status reports would not all agree. In principle they should. There is a utility in the File, Run *utl that would look for differences between the reports and use the VAL to force the TB to agree by creating IZ transactions (that is, transaction code IZ). So, I would agree in principal with your client's insistence. However, there could always be exceptions too many to list here (i.e., valuation method used, negative tiers, other corruption in the file that can be fixed using other utilities, etc.).