Conference guests; are room locations already set aside for attendees?

[typhoonlagooner]

For our upcoming trip at the GF, we were booked under a conference rate for DBF's work. I was curious if Disney already has "pre-selected" room locations for guests of a conference...

I remember reading that at CSR, most conference attendees get placed in Castias due to proximity to the Convention Center... but is this the norm for all conference resorts/guests?

I know that Disney "blocks" off rooms for conference guests in order to book under the special rate. But since the Conference doesn't physically start till Wednesday night-ish, and most will be checking in on Tuesday and Wednesday... is it "safe" to assume that Conference guests get "left overs" from whatever is still open from the weekend's check-in? Or is it the opposite... that guests looking for that specific location are "turned away" at check-in since Disney has pre-assigned the rooms to conference guests?

Any insight, experiences, or thoughts are greatly appreciated!