Trying to use SWUs to upgrade MIA-BCN-MIA later this summer. Have routinely checked EF to see if C inventory is showing as available on those flights. It is - at least 2 in each direction. Call EXP desk to confirm the upgrade before I purchase the ticket - agent says they have to be waitlisted. Tried 'hang up call back' and got the same response - with EF still showing C 2. Could EF be seeing inventory that isn't really available, or is there possibly a disconnect on the AA side where the agent can't see inventory that should be available?