We discovered some errors in Table 2 of the published paper. The observed and dereddened intensities of Hβ for NGC 6210 should be 1.396 × 10⁻¹¹ and 2.162 × 10⁻¹¹ erg cm⁻²2 s⁻¹, respectively. In addition, for IC 4593, JnEr 1, NGC 3587, and NGC 2392, we copied incorrectly the columns corresponding to the values of the observed line ratios in the red range (see Section 3 of the published paper for a description of the procedure used to derive them). Table 2 below shows the correct values of the line ratios with respect to Hβ, normalized to I (Hβ) = 100. These errors do not affect our results in any way.