C forms query

When a Company makes Interstate [IS] Purchases C FORMS have to be issued to the Vendors as CST is charged @ 2% against C FORMS, otherwise CST is charged at full rate. I have a client who has made IS Purchases @ 2% CST against C FORMS in Himachal Pradesh. At the end of the Financial Year [FY] there are situations when Vendor has dispatched material before 31st March but the plant in HP has not received the material or has received the material but bill booking has happened after 31st March. My query w.r.t. issue of C FORMS in such case is as follows: 1. If Vendor invoice date is 25th March, 2016 [FY 2015 – 2016] & the GRN is made on 5th April, 2016 [FY 2016 – 2017] & invoice has been booked by Company on 15th April, 2016 [FY 2016 – 2017] according to HP VAT/CST rules C FORMS for which FY can be issued by the Company? 2. If Vendor invoice date is 25th March, 2016 [FY 2015 – 2016] & GRN is made on 29th March, 2016 [FY 2015 – 2016] & invoice booking has happened on 5th April, 2016 [FY 2016 – 2017] according to HP VAT/CST rules C FORMS for which FY year can be issued by the Company?