What is an addendum?
A published change after release: scope, dates, criteria, or answers to clarifications. It forms part of the documents you must lodge against. Missing one is a conformance fail. Treating one as optional is how a careful firm lodges against a pack that no longer exists.
The glossary is two sentences. The bid/no-bid is whether the new fact moves an axis. A moved close date is capacity. A new mandatory is a hard gate. A changed weighting is strategy. An answer that reveals the incumbent is strategy again.
Should you ask a clarification question?
Yes, if the answer would change the call: can we conform, is the indemnity capped, may prior work on this contract be used as a reference by firms that did not hold it. No, if the question only helps the room write a prettier methodology. The buyer publishes the answer. You are not having a private conversation.
On public processes the no-contact period is live. The published channel is the only channel. A helpful email to the officer you already know is a probity event, not a clarification. See probity in public tenders when you need the rule, not the tactic.
What does a late or missing answer tell you?
That the buyer cannot or will not say. That is information. Do not fill the silence with optimism. If the question was about a lethal clause and the answer does not come, risk is unfinished. Unfinished risk is a review with a date, or a no.
Late answers that arrive inside the last seventy-two hours are how zombies start. Re-score. Do not “just keep going” because the draft exists. The draft is the argument you are trying not to have.
What if you already said yes?
Then this is a new inbound. The three axes again. An addendum does not honour a yes made against a different pack. If the room will not re-open the call, write that down. An override should be visible. Hidden overrides become culture.
If you had never said yes, a late addendum does not make you late to the gate. Read the four things again. Mandatories, liability, roster, weights. Then stop or start. Starting is bidding.