Why are there cases from SOEP-Core in some SOEP-IS datasets?

The SOEP-Innovation Sample (SOEP-IS) was established in 2011 using some of the existing SOEP-Core samples and has since been surveyed completely separately. These first samples therefore have a certain number of overlapping cases in the years from 1998 to 2011 (the oldest sample in the IS was originally drawn for Core in 1998). But all relevant data from SOEP-Core was transferred to the IS datasets. This means that basically a copy of the previously available data from these samples was created. If you already have the SOEP-IS data, you have all the available data for these cases. Over the years, several samples were added to both SOEP-Core and SOEP-IS, but these were drawn, surveyed and published completely independently of each other.