The Lumia Denim update is surely going down as one of the most confusing firmware updates from Nokia (now Microsoft). Whereas in the past, the new firmware like Lumia Amber or Lumia Black brought new features to all Lumias e.g. Call and SMS blocker, Lumia Denim's exact feature set is only for newer, PureView Lumias.

Much of this is already known, of course. For months, we have been saying that only the Lumia 830, Lumia 930 (Verizon Icon) and Lumia 1520 will see the new Lumia Camera 5.0 features brought by Denim. Now, however, Microsoft has confirmed as much on their support site.

In an FAQ message, Microsoft answers a presumably obvious question:

FAQ - I have updated Lumia Denim, but the firmware version number was not changed, why?

"Lumia Denim is the marketing name for latest Lumia software update, which is a combination of firmware, OS (operating system) and Lumia exclusive applications. Exact contents coming with Lumia Denim vary depending on the device model, and some devices are not requiring new firmware for the new features to be enabled, so firmware can in some cases remain unchanged."

This answer explains why many people are reporting their devices now say Lumia Denim even if they did not get an update. It appears that under Extras + Info, the change from Cyan to Denim can be triggered by hitting a particular OS version. For some people, this can change based on their Preview for Developer status (enrolled versus non-enrolled can change it).

The reason for that "trigger" is that some devices, like a Lumia 520 or Lumia 920, will not get new firmware. However, when they are at the right OS level – either through Preview or official Windows Phone 8.1.1 update – the phone will rightly "switch" to Lumia Denim.

For Lumia owners accustomed to new firmware releases, this news may come as a bit of a disappointment. However, up until now, not many people can articulate what it is about Denim they are expecting anyway.