Seems that it's more typical to wait for the thru count, except in situations where it's so full that they know they'll have to bump people even if the exact numbers are not confirmed, and so they start the process early - but even then, I've only seen it with volunteers at that point. Thus, if you're on a continuation and have already checked in online, you can be pretty comfortable - although because you may not be able to make yourself available at the gate 10 min. before scheduled departure if the inbound is really late, it's still not a 100% guarantee.

With the bonus credits, the BWI-CLE-MDW and BWI-CMH-MDW continuations look pretty tempting for this strategy (I've done the BWI-CLE / CLE-MDW route before with no problem).