Think about that, almost no-one serves on just their orginal engagement.
There may well be conditions tied to promotion, course amortization, re-engagement etc etc. May be difficult to avoid without bailing out.
A good point.
Some advice which worked well for me for 27 years.
Take responsibility for your own career. Do your homework and know the facts regarding your terms of service. Treat crewroom scuttlebutt, barrack room lawyers and chain of command bull with equal scepticism. As pointed out above, things change - quickly and frequently. Keep the big picture in mind and make the changes work for you.
An example of two real NCO aircrew (many were in the same boat)...
Circa 1990 and cue the option to sign onto the new terms of service or retain "reserved rights".
Young Sergeant A read the blah, went to the interview and thought screw this what I have I hold - I'm sticking with reserved rights. Thus confiming him his original financial terms of service, but rulling out the prospect of further promotion (even though he would get the money when due). PS He had already signed on since in those days NCO aircrew were signed up to 55 in their first tour.
Young Sergeant B went with the command plan and opted into competitive promotion.
Things change....rules change....circumstances change.
Not so young Sergeant A is promoted, without loss of rights. How did that happen? Answer...operational necessity. In other words, our train set, we do what we want.
Much older, unable to get promoted and extremely bitter Sergeant B leaves.
Fast forward to 2010. Young at heart
Master WSOp A has played his hand with style and panache...well done that man.
PS Neither one of them was I.