Why now? they are in Greece from more than 10 years...
They were expecting the Turks arrival in any minute, so they spared the missiles for them...
(Czech/Slovak army still not fired any S-300 missile since fielding it in 1988... ... what about the Bulgarians?)
To be on the realistic side... ... the shelf time (10yrs) of the missiles is started to be expiring. Some of those will not be sent to mid life service. (cost saving)
