Self funded Experience with RDS & PBM rebate factors

Anyone know of any standard tricks when evaluating experience from a self-funded group that uses RDS? Is there some kind of calculation or standard % amount that people assume when evaluating the claims costs to get a monthly premium cost on a per member per month basis?

Say for example I’m looking at company xyz and they have 541 members. The company offers a self-insured EGWP plan to the membership. They’re looking to off-load the risk to free up some capital reserves. The company policy holder hands you an experience file. Included is:

Drug Name
Pharmacy ID
Fill Date
Paid Date
Drug Name
Scrambled ID
Quantity Limit
Tier Indicator
Coinsurance Amount Paid
Deductible Amount Paid
Plan Paid

What you were able to confirm is that this group is using a RDS for their self-funded plan. They want to move away from that. Does anyone know how you would calculate a PBM’s rebates, and what would you consider to be a normal RDS % received in order to help whichever carrier you’re working with come up with the most compelling premium offering they can.

First Q: what is “RDS”? I might know it by a different name.
Second, a carrier should already have a system to come up with an estimate of Rx Rebate based on the past Rx claims of the group. Or, it will state, “every group gets $X/rx claim or $Y/rebate-eligible Rx claim.”

RDS = Retiree Drug Subsidy. I’m no expert, but I believe it is a subsidy that plans receive if they offer retiree coverage. It has mostly been replaced by EGWP because EGWP has more favorable tax incentives.