When Jason passes his copy of "Istanbul Iliad" to Agatha over their chess game, the cover is towards him. The shot changes, and the book has reversed so now his back-cover bio is facing him.
The copy of "The Purple Streak" Sullivan leaves for Haslet-Wood has Agatha Pollen's name on a (peeling) label on the spine. Presumably the book is actually Rupert Croft-Cooke's 1966 work of the same title.