Good fun. I think we can work that one out. 'Truly Yours' won UK awards in 1971 and the UK trials were three year trials. So it had to be bred three years before, which puts it back to being bred before 1968. The pollen parent is more likely to be the Tantau's 1956 Stella, rather than the Gaujard 1974 Stella, or Trantau's 1979 Stella.
I've altered the bred date from 1971 to <1968 and added that parentage. Thank you Goncmg.