What's the difference between an attachment and appendix relating to which may not require a contract modification if it's updated in the future?
I could not find a definition of "appendix" in the FAR/DFARS. However, I have seen where solicitations provide information and guidance to potential offerors in an appendix to the solicitation. For example, if the Government would like to provide offerors some illustrative examples of different types of transactions, they could provide this guidance to the offerors in an appendix to the solicitation. The FAR does not require this type of information to be provided to offerors in an appendix. If the Government wanted, they could have provided the same information in an attachment to the solicitation. However, the term "attachment" normally connotes a document that is intended to be a part of the contract when it's awarded. If it doesn't need to be included in the contract in order to eliminate any confusion, it's probably better to refer to the document as an appendix to the solicitation. Once again this is not required by the FAR, but how I've seen it done in the past. Also, there is not one definition of an attachment for all of DOD nor a single way to properly use this document. DFARS 204.7101 does define attachment (See DFARS 204.7101 provided below for convenience), but this definition only applies to the establishment of contract line items, is instructional, and does not have any legal effect on contract interpretation at the Boards of Contract Appeals or the Court of Federal Claims.
Other than how I described the difference between an appendix and an attachment to the solicitation, I'm not familiar with any other instances where an appendix and/or attachment are included in the same contract. As far as the need for modifying an attachment (or an "exhibit" or some other type of contract document or part) to the contract, the key is looking at what is the purpose of the document. If it's a legally binding document (no matter what it's called) which could impact cost/schedule/performance on the contract, then it's absolutely essential that the document be kept up-to-date (by contract modification(s)) to protect both of the party's rights under the contract. As for the courts, I'm not aware of them making distinctions between attachments and exhibits, so I would assume they wouldn't do so between an attachment and another document that's referred to as an "appendix" in the contract. In my mind, it's not as important what you call the document (e.g. "attachment" or "appendix") as it is to understand the purpose of the document. Does it describe or impact the rights, duties or conditions of performance? If so, then the document is legally binding for both parties and needs to be kept up-to-date by way of contract modification(s) if the document changes.
DFARS 204.7101 Definitions “Attachment” means any documentation, appended to a contract or incorporated by reference, which does not establish a requirement for deliverables.
FAR 52.215-8 Order of Precedence-Uniform Contract Format.
As prescribed in 15.209(h), insert the following clause:
Order of Precedence-uniform Contract Format (Oct 1997)
Any inconsistency in this solicitation or contract shall be resolved by giving precedence in the following order:
(a) The Schedule (excluding the specifications).
(b) Representations and other instructions.
(c) Contract clauses.
(d) Other documents, exhibits, and attachments.
(e) The specifications.
FAR 52.212-4 Contract Terms and Conditions—Commercial Products and Commercial Services.
(s) Order of precedence. Any inconsistencies in this solicitation or contract shall be resolved by giving precedence in the following order:
(1) The schedule of supplies /services.
(2) The Assignments, Disputes, Payments, Invoice , Other Compliances, Compliance with Laws Unique to Government Contracts, and Unauthorized Obligations paragraphs of this clause;
(3) The clause at 52.212-5.
(4) Addenda to this solicitation or contract , including any license agreements for computer software .
(5) Solicitation provisions if this is a solicitation .
(6) Other paragraphs of this clause.
(7) The Standard Form 1449.
(8) Other documents, exhibits, and attachments.
(9) The specification.