When a cluster containing unknown links receives an overall vulnerability level of Ambiguous or Unknown, the analysts must decide whether or not to expand those unknown links. This is analogous to expansion in the Single Failures Analysis stage (see Expand unknown links).
Note that it is not always necessary to expand unknown links. If the analysts think that the effort involved in expansion is too large, or that it will not lead to more accurate or insightful results then expansion should be omitted.
Expansion adds new components to the diagram. These new components need to analysed for single failures. This means that part of Stage 2 needs to be redone for these components. It also means that some clusters receive new member nodes. The analysis of these clusters must be revisited.