I have an external hard drive hooked up to a iMac. Its been doing Time Machine backups since 2011. When I tried to restored my contacts (I'm running Yosemite - I previously had Snow Leopard) I can go only go back less than a month. Would upgrading to Yosemite block my ability to restore files when they were the hard drive had Snow Leopard on it? When I manually look at the dates a backup occurred I can see back to 2011. I can also see these dates when I enter in the Time Machine. Any suggestions on why I can't restore from a further back update is appreciated. Thank you for looking.