From my recollection, I believe you are a Silver member. I am too.

In my experience for Silver members, although op-up can occur frequently, it is never actually processed more than 4 or 5 hours before departure. I think you're talking about a flight that's many days or hours out, and in that case there's no way you've been op-uped this far in advance.

Usually if I OLCI, I will get an Economy class seat number and later on it will change to Business nearer around 4 hours before departure if I'm getting op-up. Or sometimes it happens as late as boarding time.

Also, I've never ever had my assigned seat taken back for any reason except op-up. I think once an SL/GO books, they won't give that seat away to a DM even if they want it.

Aircraft change is also possible though in my experience when they change they aircraft, their IT automatically assigns you a new seat of similar type if possible. Maybe in your case it was not possible to be automatically processed.

I'm sure if you call in they'll be able to answer you.