In this paper, we present the outcomes of the calibration efforts of two Baltic energy system operational optimization models developed in different open-source modelling frameworks. While there are a number of similarities between both approaches, there are also several differing assumptions, simplifications and data selection choices employed. Through continuous calibration we find a state of both models in which its outputs replicates the actual historical power system operational data of the year 2020 with satisfactory accuracy. Nevertheless, there are select outputs which have more notable differences either between both modelling approaches or with the historical data. We discuss these deviations and their possible reasons. Overall, the calibrated models provide a robust foundation for future scenario planning and analysis of the Baltic power system and development of the Baltic region.