23 CFR § 636.403 - What information may be exchanged with a clarification?
(a) You may wish to clarify any aspect of proposals which would enhance your understanding of an offeror's proposal. This includes such information as an offeror's past performance or information regarding adverse past performance to which the offeror has not previously had an opportunity to respond. Clarification exchanges are discretionary. They do not have to be held with any specific number of offerors and do not have to address specific issues.
(b) You may wish to clarify and revise the RFP document through an addenda process in response to questions from potential offerors.