Hi Ellen.
How great you have a bluebird pair. Up here in NW Ohio that would be very normal. Often for the first nest my bluebirds build it and then wait. I’m not sure about down there. So it could she normal or they could have decided on another nestboxes somewhere else but my guess is that they are still planning on using that. Time will tell. Do you have a predator guard on your pole? It’s a must down there where you have rat snakes etc.
Tammy