Q. Is it necessary to continue repeating the auxiliary had after its first instantiation when writing a complex sentence with some of the verbs in the pluperfect: “She had taken many rides in the train and [had] seen many sights, sights that [had] awakened her curiosity, but what [had] most intrigued her . . .”? If not, it seems the reader would have an ambiguous idea about where the event is situated in time.
A. This is a thorny issue, especially for fiction writers. For a detailed take, see “ ‘Had had’? Flashbacks and the Past Perfect,” in Fiction+ at CMOS Shop Talk.