This was brought to your notice by others too, but none of our device received the update in India yet. Now, a nicely done screenshot comparison of before and after scenario of the Lumia Denim update shows that Lumia 520 receives only the OS update to 8.10.14219.341 and firmware version remains unchanged. The Lumia Cyan name changes to Lumia Denim, though in Extras+info.
We reported a “funny bug” that was already changing firmware name in the “Extra+info” to Lumia Denim, if you disable preview for developers. This doesn’t look like a bug anymore and may be with OS version updating to 8.10.14219.341, firmware name automatically changes to “Lumia Denim”.
Lumia Denim anyways was not supposed to bring anything worthwhile to any other devices than Lumia 830, Lumia 930, Lumia 1520 and Lumia Icon. So, for those on latest version of developers preview, which is 8.10.14219.341, there is hardly anything to look forward if you have any other device than Lumia 830, Lumia 930, Lumia 1520 and Lumia Icon. You mayn’t even get the update, if you are on developer preview and have devices other than Lumia 830, Lumia 930, Lumia 1520 and Lumia Icon.
For those who are on Lumia Cyan, and rocking a Lumia 830, Lumia 930, Lumia 1520 and Lumia Icon, you need to read both Lumia Denim + Windows Phone 8.1 GDR1 changes on our dedicated page. Otherwise if you have Lumia Cyan on any other device, check our dedicated page for only Windows Phone 8.1 GDR1 changes.