The licenses of for OS X are purchased separately from those for Windows and Linux computers.
Therefore, you can purchase as many trial/release licenses of for OS X as you want, regardless of the number and type (trial /release) of licenses of for Windows/Linux that you have. Obviously, you can also contract trial/release licenses of for OS X only.
Additionally, there is a specific section to configure the protection for Mac computers, separate from the options for other operating systems.