Acoustic source terms from high-fidelity simulated data of a rectangular supersonic jet with chevrons are found from Goldstein's generalized acoustic analogy. A statistical description of the flow field is established in detail including an in-depth look at first, second, and fourth order statistics. Fourth order correlation statistics are fit to previously used acoustic source models. Specifically, this paper performs a detailed analysis of four different models: the Gaussian model, moving-frame model, fixed-frame model, and modified-distance model. These models were previously used to describe correlation data from axisymmetric jets. In this paper, we assess the accuracy of these models in the con- text of highly complex nozzle shapes. The latter three models are found to be similar in accuracy, while the Gaussian model is found to be a poorer fit. This paper also investigates the theoretical underpinning of reduced-order acoustic source models by testing the assumptions of quasi-normality and statistical axisymmetry. It is found that the flow field is not quasi-normal in the axial direction but is however quasi-normal in the transverse directions. Our analysis also shows that the flow is locally statistically axisymmetric close to the edges of the flow field but not near the center.