What is an occurrence policy?
An occurrence policy covers claims against the insured if the incident that gave rise to the claim occured when the policy was in force, regardless of when the claim is reported (even years later). Therefore in an occurrence form policy the purchase of a tail is not necessary when the policy cancels or expires.
An occurrence policy protects the insured, up to the coverage limits, against professional liability claims arising from incidents that occur when the policy is in force, regardless of when the claim is reported. It is not necessary to purchase tail coverage when an occurrence policy is cancelled.