The business analyst should review the version control history to understand which user stories were modified by the project lead. Version control is a system that records changes to a file or set of files over time so that you can recall specific versions later. Version control can help track who made what changes, when, and why.
It can also help compare different versions, merge changes, resolve conflicts, and restore previous versions.
The business analyst should use a version control system to store and manage their user stories in a repository and review the version control history to see the edits made by the project lead. Reviewing the approval history is not a good option because it would only show who approved or rejected the user stories, not who modified them or how. Reviewing the change sets history is not a good option because it would only show what metadata components were deployed or retrieved between orgs, not what user stories were modified or how. References:
https://trailhead.salesforce.com/en/content/learn/modules/org-development-model/get-to-know-org-development