Comparison of blue-end optical spectra obtained in 2010 November, 2011 July and 2012 July, after the resolution of the former has been degraded to match that of the latter two spectra (which themselves differ in resolution and wavelength coverage; Sect. 2). Prominent transitions are indicated as are the I-band magnitudes on the dates of the observations. Following the line identifications of Zickgraf et al. (1989), additional weak emission lines from low excitation metallic species such as Ca i, Cr ii, Fe i, [S ii], Si ii and V ii are not shown for reasons of clarity.