Access and mirrors
All addresses resolve to the same market. Before entering a password, check the address in your bar against the one the login captcha prints. See Security.
Several onions run at once. When one is flooded the others answer, and a fresh address rotates into the pool. The instruction that follows is standard directory practice: do not treat any single address as permanent. Keep the signed mirror list, not a lone bookmark, and consult it when something stops resolving. A withdrawal PIN sits separate from the login, so a stolen session cannot drain the balance on its own.
The rotating pool is a resilience feature. It only helps if every address you move to is one the market actually published, so the verification step is not optional even when you are only switching mirrors.