Comment 2 for bug 297736

A substantial part of the data work is now done. Official packages are added to the DSP table when a package is uploaded or when an official package branch is linked to series. The table was updated with the missing data from SeriesSourcePackageBranches and historic packages that are not is the current series.

There may still be a need for the virtual class when DSP are being created or Lp is working with an unsupported distro. The next step might be to rename the two classes:
DistributuionSourcePackage -> VirtualDistributuionSourcePackage
DistributuionSourcePackageInDatabase -> DistributuionSourcePackage