Hi i have just downgraded from El Capitan back to Yosemite with the help of the Apple team as i could not retrieve any of my Apple Mail whilst being on El Capitan. I had no problems before that on Yosemite. I have updated and backed up all my data on a Buffalo external hard drive each week and before each call to Apple which has always worked but for some reason, when the specialist in Apple tried to help me bring back all my data after the downgrade back to Yosemite the ex hd or Time Machine has wiped the past 2 years off my drives. I am so upset because i need to retrieve this data. I have everything up to 2013 then nothing from then until November 2015. I could always retrieve the data on any up grade but once i backed up El Capitan before reverting back to Yosemite, somewhere along the way, i have lost 2 years of data. Does anyone know how to help me. I have tried to retrieve this data using Stellar Phoenix Data recovery and Disk Drill but to no avail. I am now in the process of downloading Cistem Data Recovey as well. Does anyone know why and what has happened? No one at Apple knows or can explain to me if it is Time machine and or the ex hd.