Comment 6 for bug 163944

"most relevant" means for this

* the year it enters public domain
* assumptions shown

* but also picks a specific jurisdiction based upon IP (use geoip database)
* next level could let them set their own jurisdiction for picking copyright relevance (via cookie and/or with a drop-down)

Whatever the easiest implementation is: cookie and/or database

For the first phase keep US on Openlibrary and pdregistr.ca keep CA.