"Article 5 specifies that the allies will come to the defence of the attacked country."

No it doesn't: https://www.nato.int/cps/en/natolive/official_texts_17120.htm.

"Article 5

The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and [...] will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area." (Emphasis mine.)

What if only some NATO countries come to the defence?

@MathieuPutz This counts as article 5 being respected.

@ahalekelly that's precisely for this case that the question was asked.

https://manifold.markets/ValentinManes/will-a-nato-country-be-attacked
👆 This other question relates with the attack directly.

Ok, in my mind there's two separate questions here, "Will NATO invoke article 5 if attacked" and "Will article 5 be respected if invoked". It's your question though.

But I do feel like it could benefit from an explicit definition of "attacked"

Oh I see in that other question you clarified that a missile would count but only if it was intentional. That clears up most of the edge cases.

What if a NATO country is attacked but doesn't invoke article 5? eg the missile hitting Poland.