I submit that if one walks as much of a trail that is legally open to the public, including any authorized re-route around closures, they have thru-hiked said trail.
There will be times when parts of a trail are closed for whatever reason and no alternatives are (yet) available. You skip the closed portion and go on. It’s a thru-hike, albeit perhaps only for that given year.
On the CDT, snow (as in the southern San Juans) often forces hikers to patch together alternate routes around otherwise dangerous or closed (as in Glacier NP) sections. As long as they walk border to border, its a thruhike.
The purists among us will flip back and do the closed sections IF they are reopened or re-routed before we finish the rest and go home. Extreme purists will return another year if they aren’t.
Wandering Bob
Wandering Bob