I'm quite sure that you can not schedule any flights for an aircraft until it has been delivered. But there is an airline that I am sure is scheduling flights BEFORE a new aircraft is delivered. They suddenly have many new flights that would only be possible with an extra aircraft, yet in the Fleet List and on their Overview page it clearly says that their new aircraft has not yet been delivered.
I just had an aircraft delivered myself and the option to schedule flights, the green schedule icon in Fleet Management, was not available until I had actually received the aircraft. I have no idea how this player is doing this, perhaps it's just a glitch in the game, but I have reported them just in case they are cheating somehow . . .
. . . and in case anyone from the AS team wants to check this out, I have taken numerous screen shots for evidence, which I will be more than happy to send on to you.