Update data documentation

**Problem**
When working with lib, the error messages could be more descriptive.

**Suggestion**
Improve error handling and add detailed error messages.

**Context**
This would help with debugging and maintenance.

Start by locating the lib directory and reviewing the existing error-handling paths. The issue does not identify the documentation files, affected errors, expected wording, or tests, so clarify which data documentation and error messages are in scope. Done should include the agreed documentation updates and verification of the affected behavior.

Written by the indexing model from the issue text.