The thing to consider is that the L preview is a DEVELOPER PREVIEW. It is not intended for a "production" or daily use device, it is merely for developers to use to work on making apps compatible with the upcoming OS. Part of the intent of the developer preview is that the device will get re-flashed for any updates to the preview, or when the final OS is released, they usually won't make any accommodations for keeping data as the belief would be that the person using the image would have a backup of the info on the device, or no info at all.