Abstract: Exergoeconomic methods for complex thermal systems are often conflated in terms of their economic interpretation, applicability, and validation requirements. Building on established theories of average-cost accounting and marginal optimization, algebraic cost accounting, differentiable constrained optimization, and advanced exergy analysis are compared across four dimensions: analysis target, time scale, mathematical formulation, and validation evidence. The applicability of life-cycle assessment, carbon-responsibility accounting, dynamic inventory accounting, and surrogate models is examined, and method-selection principles are drawn from representative complex thermal systems. The review shows that algebraic methods explain average-cost formation and allocation under specified operating conditions, whereas differentiable constrained optimization evaluates local marginal responses to perturbations in continuous variables. Advanced exergy analysis assesses retrofit potential, while environmental and carbon accounting extend the assessment to resource use and environmental responsibility. When state accumulation affects the assessment results, intertemporal exergy and cost relationships must be represented. If carbon responsibility is also tracked, the corresponding inventory update rules must be specified. Surrogate-assisted optimization requires independent error assessment, physical-consistency checks, and verification of key candidate solutions. Results obtained using different methods are comparable only when system boundaries, time bases, and economic interpretations are consistent. Studies of representative systems provide a basis for selecting methods when state accumulation, product functions, or decision-variable types change, and for specifying the validation needed to support cost diagnosis, retrofit prioritization, and operational optimization.