Interesting question.
After reviewing Figure 2 together with the detailed mappings that follow, my interpretation is that the repeated letters represent the number of M.O.R.E. practices mapped to a specific Focus Area and Performance Domain intersection.
For example, Executing × Stakeholders contains four "M"s in Figure 2, and the detailed Manage Perceptions mapping shows four practices associated with that same intersection:
• Build trust with stakeholders through early and ongoing engagement.
• Be upfront with project participants about what's working and what's not.
• Regularly socialize a clear point of view on the project's progress toward value creation.
• Proactively address skepticism and reframe perceived failures constructively.
The same pattern appears throughout the mapping tables, which suggests that each letter corresponds to an individual M.O.R.E. practice.
What I find particularly interesting is that the answer does not seem to be explicitly stated in Figure 2 itself.
The relationship becomes clear only after comparing the overview mapping with the detailed mappings that follow.
If this interpretation is correct, a brief explanatory note in Figure 2 could make the diagram easier to understand and help readers navigate the mapping more quickly.
Thank you for raising the question.