A consultant is assisting a nonprofit in its data integration and mapping between two systems.

When performing complex integrations or troubleshooting why a field is missing in an older sandbox, a consultant needs a reliable reference for the NPSP metadata.

The NPSP Data Dictionary:

Historical Reference: The NPSP Data Dictionary is an official Salesforce resource (usually provided as a spreadsheet or a dedicated help article). It lists every object and field included in the managed package.

Version Tracking: Crucially, the Data Dictionary includes a column for "Introduced In" or "Package Version." This tells the consultant exactly which release of NPSP (e.g., 3.154) first included that specific field.

Object Mapping: It also provides the API names, descriptions, and help text for all NPSP-specific fields, making it the primary "source of truth" for mapping projects.

Why other options are incorrect:

Custom Field Definition (Option C): In the Salesforce Setup menu, the field detail page will show the "Installed Package" (Nonprofit Success Pack), but it does not tell you which version of that package introduced the field.

NPSP Package Details (Option A): This shows you the current version installed in the org, but not the historical release version for individual fields.

Schema Builder (Option D): This is a visual tool for seeing relationships between objects; it contains no versioning or historical metadata.