You don't need the notice from Nike to understand the scope, it takes 15 minutes to find the statute and read it. It's very simple: with 500 or more people at a SITE (emphasis) involuntarily terminated in 90 days = obligation in this case to file for phase 1 + 2 + any others in the period.
People seem to be glossing over payroll termination date versus when conversations happen. Most end dates are in May for phase 1 except H1B. WARN is not a clever rule and has been skirted by payroll timing trickery for its entire existence. Delaying notice helps companies like Nike that don't have an actual RIF plan figure out their layoff strategy after it's partly underway.
The max penalties are also peanuts and lower court action doesnt go very far, this is a checklist item for a company like Nike.