Does the multi-part external identifier identify a party or a product ? If the latter, why are you relating the parts to the party in your party_id_components table ?
Can a party have more than one product ?
Are you going to need to manipulate or query the parts of a multi-part identifier separately ?
Why don’t you provide a more elaborated example with actual values (i.e. numbers and/or strings) instead of p11, p12, etc ?