Help Regarding Sales Tax Return

We dont have to revise the Return if we dont get the requisite form from the buyer. Howwevr, during the VAT Audit, the auditor is required to give a list of buyer from whom the forms are not received, and consequently, the liability will increase on account of sales to those buyers. Our Sales tax on sales to those buyers will be calculated as if the sales to unregistered dealer and thus will have to pay tax at highest Tax slab which may be 12.5%.