We perform spectral analysis based on a suitable theoretical correlation between V-wave visibility and D-particle distinguishability following the complemen-tarity principle to verify wave-particle duality in the asymmetrical double-slit experiments. The selective interference spectra obtained in the experiments ensure the single-photon approximation in the Fraunhofer far-field condition. The results show that the theoretical interpretation following wave-particle complementarity may not be consistent with the experimental data, especially at the first main minima of the optical diffraction distributions. A dilemma would arise when one tries to revise the theoretical explanations for preserving the complementarity principle.