A project manual is published once and read many times, but it is rarely bid exactly as published. Between the day a solicitation goes out and the day bids are due, the document that actually governs the manufacturer list is not the original specification section. It is whatever addenda were issued on top of it.
This is the part of the record most often skipped, and it is where a specification position most often changes without anyone updating the section itself.
1. What an addendum is, mechanically
An addendum is a written modification to the bidding documents, issued by the design professional or the owner before bids are due. It is numbered sequentially (Addendum 1, Addendum 2, and so on), dated, and distributed to every party who registered for the solicitation.
An addendum can do almost anything a spec section can do: add a manufacturer, remove one, change a performance value, extend a bid date, answer a question a bidder submitted, or attach a drawing revision. It carries the same contractual weight as the original document once it is issued. A bidder who prices the job against the original section without checking for addenda is pricing the wrong scope.
2. Why a substitution request becomes an addendum
The most common way a new manufacturer enters a section after publication is a substitution request during bidding, described on CSI Form 1.5C. A prospective bidder or a manufacturer's rep submits the form, the design professional evaluates it against the section's salient characteristics, and if it is accepted, the addition is published in an addendum rather than a quiet email back to the one company that asked.
This detail matters more than it looks. The manufacturer who did the work of getting evaluated and approved does not get an exclusive result. Once the approval is in an addendum, every bidder on the project can use it. A rep who spends a week getting a product added to a section has, in the same motion, opened that section to every competitor bidding the job.
There is a mirror version of this that removes a manufacturer instead: an addendum can strike a name from an approved list, typically after a design professional receives new information (an updated cut sheet, a code compliance question, a reference check) between publication and bid. A basis of design position read from the original section can be wrong by bid day in either direction.
3. Where addenda are published, and why they are easy to miss
Addenda are usually published on the same procurement portal as the original solicitation, as a separate document or a separate line item, not merged back into the project manual PDF. This is the single most common reason someone reading a project manual believes a manufacturer list is current when it has already changed: the portal shows the original specification and the addenda as two different downloads, and only one of them is usually opened.
A second failure mode is timing. A portal search run today returns documents as they existed at that moment. A solicitation with a thirty-day bid window can accumulate three or four addenda over that period, and a document set downloaded on day one will not reflect an addendum issued on day twenty.
The practical habit: never treat a project manual as complete without confirming the addenda count and pulling each one. Most portals list a document count or a "last modified" date on the solicitation page; a specification section with a publish date earlier than the most recent addendum on the same solicitation is a signal to check what changed.
4. The deadline that decides whether an addendum is even possible
Division 01 of the project manual, or the instructions to bidders, sets a substitution request deadline during the bidding phase, commonly seven to ten days before the bid date. A request submitted after that deadline is typically rejected without evaluation on the merits, and the record of that rejection looks identical to a rejection based on the product itself.
This means the window for changing a section through an addendum is shorter than the bidding period itself. A manufacturer that identifies a project in week three of a four-week bid cycle may already be past the point where a substitution request can produce an addendum, regardless of how strong the case is. Reading the deadline is part of reading the section.
5. After award: a different document, a narrower effect
Once a contract is signed, the substitution process moves to CSI Form 13.1A and AIA A201 Section 3.4.2: the architect evaluates, the owner consents, and the instrument is a Change Order or Construction Change Directive rather than an addendum. The practical difference is scope. A post-award substitution changes one contractor's one project. It is not published to other bidders, because there are no other bidders left. A manufacturer that misses the addendum window during bidding can still pursue a substitution after award, but the audience for that approval is exactly one project, not every bidder on it.
6. What this means for reading a position and trusting it
A specification position read from the original project manual, with no addenda checked, is a snapshot that may already be stale. The two things worth confirming before treating a section's manufacturer list as the position that will actually be bid: how many addenda exist on the solicitation, and whether any of them touch the section or division in question. A position is not current until both are checked, and a position worth managing to has to be re-checked as new addenda are issued, not read once and filed.