I've imported a bunch of rsd files into a DataSet folder within Report Manager as well as a bunch of rdl files into folders within Report Manager. I also have a shared datasource created using the same name that was used for the datasets. If I edit the DataSet in Report Builder, I see the syntax. I can also run the query in Report Builder and see the data so it all works.
If I edit one of these reports, then click on datasource, switch to my datasource (as it's still referencing the original), test connection works. The datasets that are setup as shared show "Unknown Shared Dataset." If I create a NEW report then add a dataset, there are none listed.
I'm using SQL 2012, SP 2, Report Builder 3.0.