Autonomous Central Government Institute - 7 CPC

I was working with a PSU Bank, from where I have appeared for an interview for an Autonomous Institute advertise a 6CPC post within PB-3 Grade pay 6600/- in June 2019, subsequently, I got through all processes and got the appointment letter (with 2 years probation) in March 2020 joined in Sep. 2020. The institute has already been implemented 7 CPC except for this post. As per DoPT Guidelines for pay protection for my last salary (basic+DA) shell be protect, As per 6CPC my basic and DA is more than the PB-4's last basic salary and the current rate of DA will make entry level pay equivalent to this. now my doubts are as under : 1. how one Institute can differentiate between the posts in regular capacity i.e. some are in 7CPC and only one in 6CPC. it is not the equal opportunity to all. 2. what about my pay protection, whether it will be applicable 6cpc or 7 CPC. 3. in case institute has agree for 7 CPC in that event what will be the date of application of 7 CPC.