Your three unknown prints are in order Polyanthus (c1921), The Country Bunch (c1922) and The Chinese Vase (c1920). My husband R. is the great nephew of JHT (paternal) and directly and through his mother inherited many, many prints, including etchings going back to the 1890s.
His wife died in the 1950s and they were childless, so his collection came to Australia. It was divided between his four nephews some were sold and others I suppose dispersed through their various children. Except for some of the prints displayed at home and some sold or given away, others perished over the years, as R. was an only child the collection was virtually intact and stored away in cupboards, we even found prints in the garage. So the prints had hardly seen the light of day for about 40 years.
I found that JHT printed on different papers ie. Sweet Peas in Glass Vase is printed on like a thick sort of paper, the smaller flower prints were on a shiny cardboard, others on a more porous sort of paper. Also I came across some variations of the colour of the vases, if memory serves Nasturtiuams and Sweet Peas and possibly Marigolds. Parrots and Possum was a Christining gift given to R. by JHT that has the birds in different colours.
Would you believe we even have his original letter of recommendation and introduction to England from the newspaper he worked for here in Sydney it's dated 1900.
This last picture from Felicity from http://www.bellagraphica.com/