If you have an opinion different than one posted hear you need not contact me as often I will have a different opinion also. My intent is to try and provide both sides to the issues confronting bluebirders and to do so in an impartial manner. Last year my nest box had bluebirds actively going in and out, but when I cleaned it out at the end of the season, the nest was very clean. I can't imagine a nest remaining clean even if the eggs had been stolen.
Bluebirds leave very clean nests for the most part.
They eat the egg shells and take out all fecal matter. In this case the nest will be lined with a muddy coating. If it was very flattened, no matter how clean, you can assume all babies fledged successfully. The flatness suggests babies and parents having flattened the nest by sheer weight over the course of the nesting phase. I can't imagine a nest remaining clean even if the eggs had been stolen.