The retroactive date on a policy is the date from which business activities are insured. This can be "none" in which case all previous activities are covered; or "date specific" when only activities after that date are covered.
For your policy to comply with the RICS Rules, and be fully retroactive, then it should be retroactive to cover at least the last 6 years of activities, with no exceptions within the policy conditions. If your firm has been trading for less than 6 years the policy should be retroactive to the date the firm commenced trading. For example the policy will need to cover the work of all past directors and employees and all types of work completed in the past.