Using Gedcom to migrate from FTM on Windows to FTM on a Mac will lose data. Instead, use the utility described at
http://www.familytreemaker.com/Support/Migrate. This utility modifies the FTM file to enable it to used on the Mac. Citation test was exported in FTM 2012, but that feature was deprecated in FTM 2014 for unknown reasons. It is possible to export an FTM 2012 FTM file from FTM 2014 and then export a Gedcom from a version of FTM 2012, in order to export the citation test to a Gedcom. This method also works to export the description field on media. Your specific problem might best be handled in two steps. First, go back to your first file and use the utility to migrate it to the Mac. Second, using the Menu option "Merge", import the tree on the Mac where you added people. Use the radial option "Include only selected individuals from the import file" and then select the specific people you want to add. Those steps should preserve your original sources and also the new people you added.