Remember one important thing, factory cats will have nice welds and NO "CARB EO" numbers.
Sure, the exhaust could have been damaged and someone made their best effort
to do a weld repair, no harm no fowl, no fail in my book.
you can do anything you want after the cat, not even a smog issue unless you add an additional cat after the last cat. Welding on a exhuast system is a normal repair that is made all the time. If it was bubble gum or glue then you have something worry about.