In mills with a side-mount tool changer, you can set up tool numbers higher than the number of available pockets. This way, you can keep offsets for tools that have been taken out of the machine, but you plan to use them again.
To use this, first change Setting 90 to set your tool number range. You can then assign new numbers to the tools (up to the limit in Setting 90) in the pocket tool table. The tool offset table will now also have up to 200 offsets available.