The "experimental" energies of species such as the hypothetical non-aromatic cyclohexatriene must necessarily refer to a relaxed geometry appropriate in the absence of delocalization, and cannot easily adjust for additional effects such as ring strain. However, our BEBOP estimate for biphenylene retains the low bond order (0.7363) for the strained C-C bonds of the four-membered ring, resulting in a somewhat larger estimate of the resonance stabilization energy (44.6 kcal/mol vs. 39.0 kcal/mol). In general, one should compare to the most structurally similar acyclic species available.