No, creating a new catalog as a result of upgrading your LrC wouldn't result in causing the problem. The problem would present itself "if" you had a catalog that you initially began synchronizing images from and then started a separate catalog for some reason that you wished to keep images separate from your "master" catalog. Those images in the separate catalog would not be able to be synchronized. Only the images in the master catalog would be Synchronized. This would remain true even after a version upgrade.