Taxabilty in GST should be on basis of GSTR 3B or GSTR 9

Taxability is based on the business activity. The liability is discharged through GSTR 3B. 

If any liability remains unpaid on unidientified until GSTR 9, then can be disclosed in GSTR 9 and paid through DRC-03. 

Earlier through GSTR-9C independent auditor used to recommend taxes (if any missed out), now (from FY 2020-21) as GSTR 9C is a self-certification process, it would be similar to GSTR 9C. 

Interest would apply for delay in payment of taxes w.r.t time of supply.