(A moment of light relief)
One of the continual plagues of anything where somewhere has two names is people continually switching from one to the other.
Usually, this is a zero-sum game; it's moot which one you use. In a specific historical context, you can get away with one then the other in brackets (so people don't start wondering why the Danzig shipyards were important in the 1980s); here, people just tend to change the primary to the secondary and vice versa. Net result: no-one who didn't already care deeply about it tends to notice.
Sometimes, they change them all, such is their desire to expunge the "wrong" form...
http://en.wikipedia.org/w/index.php?title=History_of_Kolkata&oldid=22820...
"Calcutta, formerly named Calcutta, is the capital of the Indian state of West Bengal..."