You wanted to know how these dates are determined or from where these dates are fetched.
SAP Business ByDesign
The four dates in the report PROPRJU04_Q0002 Project Performance by Project Structure are given below that are seen in project.
Baseline Start Date shows the Baseline Latest Start Date
Baseline Finish Date shows the Baseline Latest Finish Date
Forecast Start Date shows the Latest Planned Start Date (of the project)
Forecast Finish Date shows the Latest Planned Finish Date (of the project)
Baseline Finish Date;Forecast Start Date;Forecast Finish Date;Baseline Start Date , KBA , AP-PRO , Project Processing , Problem