Filing of returns: periodic and annual submission rules, revision window, inspection rights and late filing penalty apply. Rule 12 requires assessees to submit prescribed monthly returns of production, removal and particulars, with a quarterly option for value based exemption eligibility; special invoice summaries are required for pan masala manufacturers containing tobacco. An Annual Return for the preceding year is required, subject to exemption by notification and applicable to export oriented units. Proper officers may scrutinise returns and demand records; assessees may file revised returns within prescribed windows, and late submission attracts a per day penalty with a statutory maximum. Extension of time may be granted by the Board or Central Board.