Payment Instructions

I'm researching a payment issue and came across a series of DFARS clauses under the general heading "payment instructions." These clauses all start with 252.204 and range from 252.204-0001 through 252.204-0011. I cannot find these clauses in my various searches of the DFARS. All the clauses I see start with 252.204-7xxx. Yet, at least one of these secret clauses is incorporated into my contract, so apparently my company is required to comply with the associated payment instructions.

I'm sure I'm missing something obvious. Can somebody please tell me why I can't find these contract clauses in the DFARS list of contract clauses, and what the prescription is for their use?