This is advice for attorneys working on their first insurance coverage cases.
If you represent the insurer, ask the insurer for a certified copy of the insurance policy or policies for every coverage year that may be triggered by the loss. Do this as soon as you receive the case. Certified copies are put together by the underwriting departments at the insurance companies, and it can take months for them to do it. I have had many experiences where the policy put together by the adjuster contains the wrong forms, is for the wrong policy years, or is just incomplete.
If you don't represent the insurer, or if other insurers are involved in your coverage dispute, immediately serve a request for production of documents requesting a certified copy of the policy or policies. You don't need to wait until you have an entire request for production of documents on all issues of the case; you can do your first request and then do a second, complete request when you are ready.
When you receive your certified copy, compare the forms listed on the schedule of forms and endorsements to the forms you have actually received. If there is a discrepancy, follow up immediately.
Make a copy of the policy you have received. Bates stamp your copy. When you refer to policy pages in motions (or memoranda to file), you can do it by Bates stamp numbers instead of making the judge flip through a dozen strangely-named forms trying to figure out which one you are referring to.