you need 3 eVouchers to upgrade from Business on transatlantic flights. It used to be 2, but now it is 3 and possible from all fare buckets PZDCJ
The trouble is that you cannot find out for sure before making the booking whether the upgrade will be confirmed straight away or be waitlisted, and sometimes the WL for F upgrades won't clear until the day of departure or close to.
The availability today is just a mere indicator, but May/June are still months away and the routes likely busy towards the summer.