What we did was to base it upon the customer information given and whether or not the customer was in front of us. For example, a P1 (or B1 for business customers) rating assumes that the customer is sitting in front of us, they have the required information and we have verified it. A P2/B2 would mean the customer wasn't there, but we had the required information and could verify it (perhaps the customer dropped it off, or faxed it), P3/B3 would mean the customer was there, had the required info but it couldn't be verified, and so on....(if you want more specifics, pm me and I'll get something to you). A "5" rating wouldn't necessarily be bad - it would mean that you had nothing and the customer wasn't there. For a business that would probably be suspect, but a P5 for an individual might be for a minor, or legally incapacitated person who has no ID and you never see when opening the account.
Hope that helps.
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Opinions are mine and never to be taken as legal advice!