The inﬂuence of the dimensionality of the performance matrix and the duration of the performance data series on the power performance assessments by the IEC/TS-62600-100 and IEC/TS-62600-102 speciﬁed methodologies are assessed using time-domain model simulations of wave energy converter. The wave energy converter is a two-body self-reacting point absorber with an optimum passive damping power take-off. A 3D performance matrix approach, where the additional dimension is spectral bandwidth, is shown to improve the accuracy of mean annual energy production calculations. In the IEC/TS-62600-100 analysis, the 3D approach reduces error 2-3% and in the IEC/TS-62600-102 analysis, the 3D approach reduces error 10-15% The duration of the performance data series is shown to be more critical for the IEC/TS-62600-100 analysis; However, the criticality is reduced when a 3D performance matrix is used. Lastly, the duration of the performance data series is shown to be less critical for the IEC/TS-62600-102 analysis.