If you drop existing databases for BDSSA and use a clean set of databases, it is as good as working with a new install of BDSSA. In this case, I beleive all the data from your BL database will be transferred.

However, you can also limit the amount of data that gets transferred by setting a cut off date in the ETL script.

Take a look at the section named "Specifying ETL cut-off dates using set_etl_cutoff.nsh" in BDSSA Administrator Guide for more information.

It should be whatever is in the bbsa db when you run the etl.