The "arising prior to" and "arising on or after" refer to the policies, since that is the closest term to the modifier. So if a policy arose on or after the effective date, the liability is the buyers, if the policy arose before the Effective Date, the liability is yours. The way its written, you'd be responsible for any paybacks on any policies arising before the effective date, even if you didn't actually get the commission on it, because the commission was received after the effective date. (See the first provision of section v.)
That provision seems to be to your disadvantage, in that sense.