There was some discussion in the 18F Slack, which boils down to the following example:

Suppose you are building System X on top of cloud.gov. Let's take an arbitrary control family, like contingency planning. cloud.gov may have its own contingency plan, but that doesn't mean that System X does. We need a way to indicate what controls (or control family? or control implementation?) family can be inherited and thus take care of the requirement for System X, and which System X is required to fulfill on top of cloud.gov.

@cmc333333 ran into this problem when trying to do gap analysis, almost immediately after setting up an opencontrol.yml in 18F/epa-notice#424:

that leaves only

Number of missing controls: 1
NIST-800-53@SC-12 (1)

When diffing with LATO. does that seem right?