Pay protection

Sir..... Here is my question. I was granted back date promotion in my previous deptt. And my deptt has fixed my pay as 14420+4600 in the pay band 9300-34800+4600. And at that time joined another deptt in the scale of 5200-20200+2800. I hv been told that my pay will be protected. I m submitting my calculations plz guide me.... whether I m correct or not.. 14420+4600=19020 19020-2800=16220 My pay after protection will be as under 16220+2800=19020