That... depends on the precise geographic location of any retaliation. The participation of a NATO state in a collective self-defense action with a non-NATO state under UN Charter Article 51 rights, outside of NATO operations, does not itself limit the applicability of Article 5.

And even if it didn't trigger Article 5, well, most NATO actions have been initiated as a result of Article 4 process, not Article 5 commitments. And an attack on a member’s forces in the Euro-Atlantic region but outside of the precise area covered by Article 5 commitments would arguably be a more serious Article 4 issue than the ones that have resulted in NATO interventions.

Really? Does it have to be unprovoked attack? And what exactly means unprovoked? Does having a peace mission in some neighbouring country and defending yourself there counts as provocation? Who decides that? And do you think that the definition that would be most geopolitically convenient at that moment wouldn't be chosen?