Tu najdes odpoved na otazku povodneho Yosemite / resp. Systemu pri kupe/
https://support.apple.com/sk-sk/HT201314
Konkretne :Which version of OS X is installed by OS X Recovery?
If you use the Recovery System stored on your startup drive to reinstall OS X, it installs the most recent version of OS X previously installed on this computer.
If you use Internet Recovery to reinstall OS X, it installs the version of OS X that originally came with your computer. After installation is finished, use the Mac App Store to install related updates or later versions of OS X that you have previously purchased.