It is unfortunate that so much of our rose literature is so bereft of footnote, endnote or helpful reference. Two of the many things I admire about GST are that he did include some clues about his sources and that, when he realised he was responsible for an error, he set about acknowledging and correcting it in print. I have always wished more rosarians were prepared to do the same so that we might have an easier task of sorting fact from opinion.
In his chapter on The Hybrid Musk Roses in 'The Graham Stuart Thomas Rose Book', he mentions the fact that coloured plates of the Hybrid Musks are conspicuous by their absence ("Apart from one poor picture of an over-coloured 'Felicia' in the National Rose Society's 'Annual', I have found no good portrait other than that recorded for 'Danae' [The Garden, 1913, page 254]" and refers us to his own article in The Rose Annual,1968 and Hazel Le Rougetel's 'A Heritage of Roses', 1988.
Jack Harkness also has a chapter on Pemberton in 'The Creators of Heavenly Roses'.
I'll check these refs later today to see if there is anything there about 'Thisbe' and will also see whether copies of 'The Garden' from that era have any light to shed.