Mr. Vaurn,
As per Sec.3(b) read with Sec.6(2) provides for Interstate sale by transfer of documents of titile to goods during the movement from one State to another. The document of title generally called like Lorry Receipt, Railway Receipt, bill of lading and Air way bill. During the course of interstate movement of goods, such document of title can be endorsed to another dealerat any time before taking delivery of goods from the carrier. So in order to clear the mattter it is stated that endoresment can be done on document of title any time after the goods are handed over to carrier but before physical delivery is taken at destination from the transporter.
In your case Company A in MP is delivering the goods to carrier in M.P and obtains lorry receipt / Railway receipt or such document of title raising its invoice to Company B after collecting 2% CST along with E-1 form. Company B endorse the document of title affixing its seal and signature without unloading the goods from the carrier and issue invoice not collecting CST to Company C at AP. The company C would issue C form to B and in trun B would issue its C form to A .In order to claim exemption B would submit C form recived from company C and E-1 form obtained from A before its assissing authority. This is the procedure to be followed while conducting sale in transit under CST Act, 1956. Since the issues stated in exemple are not clear, I declained to answer the same.
Devananda Narasimham.