There is no requirement that you retain copies of all pages, BUT, you must retain evidence of compliance with regulations that apply to any of the content of your pages. That means no retention of general info like business hours and branch locations. On the other hand, rate boards, application forms, and certain product details are subject to such things as Regs. B, Z, and DD & you must be able to prove that your advertising meets the standards of whichever reg. comes into play. You can determine the need for retention on a page-by-page basis or simply grab the whole site if that's easier.
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...gone fishing.