Tax Deduction at source

My client is a Building Contractor. His company adopts the percentage of completion method. Progressive running bills are raised and prorata advance recovery is done on each running bill. Bills are accounted on merchantile basis. The gross value of the bills including the amount retained by his customer is accounted as contract income. Tax is deducted by his customers on payment made towards the said bills after deducting tax at source. He is  claiming a refund due with the contract amount by submitting the TDS certificates issued by his customers. I want to know whether he should be given full credit of TDS deducted by his customers in the respective year of deduction?