although you might think you do, you really dont need (or want) to have a primary key structured in the way you mentioned
have an auotnumber key, which can then be used to link records in other tables - now if you THEN want additional data in the record, such as the date it was created, or a reference number, then add these in as separate fields. (note if it is unique, the reference number could be used as the primary key - but then you will probably get hung up on making a sequence intact, and stuff like that) - the reference number, and date can always be used to sort your data - the primary key is there to link your data tables together
there will be some discussion on here about whether autonumber primary keys are/can be superfluous - all i can say is i tend to use them, and it doesnt hurt.
the thing is not to get to hung about the structure of the primary key - if you are getting concerned, then you are probably talking about attributes of the entity, and not the primary key. - especially if you have repeated segments of the key - in many applications, primary keys would not necessarily be visible to the user, so it doesnt matter what they are!