In August when Microsoft detailed the Mango app submission process, developers were told that once Mango version of their apps are submitted, NoDo version cannot be updated. This led to the serious discussion among developers to whether submit their Mango apps to the marketplace now or not, because any changes to NoDo version is impossible. But to the rescue, Microsoft listened. Microsoft today announced that developers can publish updates to both the 7.0 and 7.5 versions of their apps. This is a great news for developers.
From Windows Phone team blog,
We heard you, and are happy to report today that by the end of October we will enable functionality in App Hub that will allow you to publish updates to both the 7.0 and 7.5 versions of your apps. Knowing that on average people update their apps every three to four months, this October timeframe provides assurance that you that you can submit 7.5 apps today and still have access to your 7.0 app well before the next update is required. Thereâ€™s no need to wait!
Microsoft will now add an graphics overlay as seen above indicating new features of the recent version. You can find more details on maintaining both version of the apps, their metadata,etc on Windows Phone team blog.