vat return

now Mr.x is filing VAT Return for the last quarter Jan10-Mar10. BUT

Mr.X finds difference in the last 3 quarters(apr09-jun09/jul09-sep09/ oct09-dec09) returns filed with the sales tax and the current accounts data. the has purchase in inc/dec.

if we revised return all the three quarters now, is there any chances of scrutiny and is there any time limit to file revised return.