This is all incredibly helpful, thank you. So I'm guessing seats.aero doesn't actually know the number of seats available, just that one or more seats is/are available. When I checked pointsyeah for the same dates, it shows me only one first class seat available for award booking, consistent with what y'all are saying and consistent with what Emirates shows on their website.

Might go ahead and book J. Will check to see if first class seats are even available for that day (for purchase) on expertflyer. And then hold out hope that upgrade option from J to Z is available at a later date. Worst case will travel J. This is for the ATH EWR route, which will have upgraded 1-2-1 config starting in Feb 2025, so still should be a good experience.

Thank you all!