1SA is the lowest (least amount of packaged options) of the available option packages. Each subsequent package added more items. So 1SB included everything in 1SA and a few upgrades and 1SC included everything is 1SA and 1SB plus even more options.
Typically, the individal items in an option package were not available by themselves. You had to get the option package just to get a specific item. The cost of the upper-level packages included the costs of the packages below it.