Fragmentation is having multiple incompatible versions of the same thing, namely, two apps which both have a Facebook chat.

Now there'll be one app with Facebook chat and one Facebook app without chat. No fragmentation.

There is absolutely fragmentation! What used to be one app is now three: Facebook (minus chat), Paper (with chat), and messages (only chat).

This time last year 2/3 of those apps did not exist. They have fragmented the user experience into entirely different apps. The concept you are mistaking for fragmentation seems to be the concept of duplication'. Right now all three apps do messaging and they will soon be reducing that number to two (Messages and Paper).

Not sure your math checks out…

Well I'll give you this example.

If Facebook would release 3 Facebook apps, where each has mostly the same features, but slightly different, and on top of that each requires a different user/login, that's definitely fragmentation.

Say, you can argue WhatsApp and Facebook Messenger, or Instagram and Facebook picture posting represent fragmentation for Facebook, as they do mostly the same thing, but are each in their own space and with their own APIs and their own users etc.

Another example. iOS having lots of apps in one App Store is not "app store fragmentation". But Android having many separate app stores, many apps in each being the same (but tweaked or different versions) is "app store fragmentation".