I am happy to report I could upgrade from Z to A on LX92 to GRU about 3 months out, with my e-vouchers expiring end of December.

I had not been able to upgrade J>F with these evouchers lately so I felt pessimistic but with a lot of flexibility on the trip, I booked flights on several days showing F8A6.
The Upgrade Award tool on M&M showed availability with miles for one flight, but I couldn't apply the voucher online. A quick call to Basel solved the issue and the upgrade confirmation was soon in my mailbox.