Just to make sure that we are on the same page and i tried to write as clear as possible(my English isn't always the best) earlier.

dabee69 im talking about the actual booking class which has to be available for the upgrade to go through, did the call center specify that it's J instead of Z or were they vague and could have spoken about the end result: upgraded ticket, which is J after the upgrade has gone through?

I don't know if you are getting my idea guys but i found this interesting. It would be great if it would be like that "If there J availability you can use voucher" because there is tons of availability compared to Z which they don't even load to various routes GDS(?)

Could it be also that agents are just pushing the upgrades through and not really checking the availability that much?