Summary: For works contracts spanning the July 2017 GST rollout, the key is the physical execution date. Work completed before July 1, 2017, is generally taxable under the old VAT/Service Tax regime (per Section 142(11) of the CGST Act), while work executed after that date is subject to GST. Your appeal should provide audited documentation bifurcating the work completion timeline to clarify which portions are subject to which tax regime.