The IPKat challenge; when was a company formed?

IPKat, noted "the celebrations of IBM occasioned reflections on the handful of companies that have succesfully remade themselves multiple times. How many such prominent companies are there and how far back do they reach in time? One such list was recently suggested by Bloomberg Business Week, which described the following companies: Siemens, Western Union, Diebold, AT&T, Ericsson, NCR, Nintendo, Eastman Kodak, Xerox and IBM. To that list let me throw in GE, Nokia and HP. "

IPKat challenged its readers to "place them in chronological order, from the oldest to the youngest?"

The first respondent had an order which included -- GE - electrical goods since Edison
AT&T - telegraphy and telephony
Western Union - telegraphy and money transfer--

which brings up an ambiguity in the question. Are we talking about the named company per se ("GE") or do we include its predecessor? Edison had companies BEFORE GE was formed, and GE threw Edison out. The American Bell Telephone Company went after Western Union (aided by Edison) long before AT&T was formed. [see
Is Lemley right about Bell and Gray? ]

Similarly, are we concerned with the formation date of Xerox, or of Haloid? See Chester Carlson and Xerography