It is spelled out in the contract, each contract signed is different depending on the mood of Mgmt at the time - even if you saw the contract of someone signed on last month, that does not mean it is the same as the one signed last year.
As far as the "brother-in-law" comment - HA HA HA. Go ask some of the professional instructors as if they feel they are in the same club as the flexes and LCA's, etc.
And, last, any pro who refuses to come to the line right now only loses the seniority from the few other internals who do move to the line. Even if they delay the move, they will more than likely be in a class before any external new hires when hiring does start. My take is the loss of 2 or 3 numbers is not worth the risk of BLG reduction and/or furlough. That is just my take.