Hi I am putting a Macbook in to get a drive upgrade. The existing drive is El Capitan and the store issues the new drive with Yosemite (that's their policy - they say it's the most stable of the 3 and I can upgrade once it's on if I like). The worry I have is that the Time Machine backup will be made with El Capitan and then they'll be using the migration assistant in Yosemite (an earlier OS) to read in the apps and data from that backup. This doesn't seem safe to me. I always think you should go from older to newer. Does anyone know if this is even possible ? Will Yosemite not balk when it sees the later version backup and refuse to read it ?