The most important result of this work is a quantitative experimental solution to the problem of classifying the electronic spin state of organic diradicals by ESR spectroscopy. The rich ESR behaviour observed for these particular Chichi-babin radicals, AAF and FAAF, has allowed such a solution to be developed systematically. To start with, a quantitative analysis of the liquid state cwESR spectra provided the first hint that liquid solutions of FAAF contain a mixture of species with different spin quantum numbers (doublets and triplets). In fact, the doublet component only appears distinctly in the ESR spectra and cannot be conclusively gleaned from the other characterisation techniques used in the synthesis (see SI). Further and clearer evidence supporting the presence of this admixture was obtained from analysing the FID spectra, the nutation spectra, and one-dimensional ENDOR data. However, the technique which offered the most direct discrimination between the two components proved to be hyperfine-correlated ENDOR. This latter experiment relies only on the nuclear spins acting as reporters of the electronic spin quantum numbers. The interpretation of the hyperfine-correlated ENDOR data in figure does not require overly parameterised simulations, or an external reference for the spin quantum number. It is therefore applicable to a wider array of PAHs, and other species, with unpaired electrons, beyond FAAF and AAF. The doublet component present in solutions of FAAF is a fluorenyl-based monoradical, akin to AAF, arising from a non-trivial interplay of many variables, such as: interactions with molecular oxygen, with other molecules of the same type, with the solvent, and with light. However, it is now clear that the 'doublet impurity' noted by researchers working on these and similar systems for the past 53 years is, perhaps, not an impurity at all.