API/BUG: Handling Dtype Coercions in Series/Index (GH 15832)
 - [x] closes #15832
 - [x] tests added / passed
 - [x] passes ``git diff upstream/master --name-only -- '*.py' | flake8 --diff``
 - [x] whatsnew entry

Hey @jreback , need a quick help here. I was able to raise an overflow exception (case II), but I wasn't able to raise it on case III. Can you help?  Thanks