If like me you own a Windows Phone you might have already installed the Windows 8.1 Developer preview. Perhaps you also experienced some unpleasant bugs and tried a full reset to fix this. You could then have read that Microsoft released an update on the 15th of May which fixed many bugs... But wait phone up update says you are already on the latest version and yet you only have version 8.10.12359.845 not the all singing all dancing 8.10.12382.878
In order to get the new update you need to have the developer preview app installed, which you inconveniently deleted during your factory reset. Good news is after a quick reinstall you will be able to select update phone and grab the new and improved developer preview.
Hope this helps anyone who is also sitting there scratching their head wondering why they aren't finding the new 8.1 update.