I have 5 IOS devices with 3 of them stuck on iOS version 12.5 (older iPhone 6’s), using Roomie 6.2. The other 2 are on iOS 14.8 and Roomie 7.02. My primary controller is running 6.2. The newer IOS devices are able to communicate fine with the controller running 6.2. We need to have access to 5 devices since we have roomie for the most part in each room around the house. It is expensive to update the last 3 phones so they can operate on iOS 14 or greater and on your 7.02. My question is can we update the primary controller to 7.02 and then can we still access and sync the older phones still running 6.2, and gradually update as the wallet allows?
No mixing and matching of versions whatsoever is supported as documented, and could definitely lead to problems.
As you may have noticed, certainly there are cases where it works.
But officially, this is why we publish the clear update timeline. Every year moves 1 iOS version forward. This Fall with V7 that was iOS 14.5 minimum. Next Fall it will be iOS 15.X minimum. So the progression is predictable and you can time upgrades to that.
As we’ve noted many times, the best conclusion to make from that is always acquire devices with the most recent CPU possible. Apple periodically introduces devices that are abnormally up to date in terms of their CPU. The iPad Mini 6 is the most recent excellent example where the A15 CPU is more up to date than even its sister iPads and iPhones and is thus an excellent choice. Basically, you want to ensure the maximum number of years before Apple removes it from the supported iOS devices which is almost entirely determined by which AXX CPU you get. Right now, look for devices with an A15 or at minimum A14 to give you the longest runway.