According to the Longman Grammar (Biber et al., 1999), it is...

According to the Longman Grammar (Biber et al., 1999), it is dificult to identify the intended time reference for the past perfect, because the reference depends on the context. In “All of them were loved, but most had missed many of the experiences we expect children to have in their first five years." (l. 12), the time reference for the past perfect verb phrase is: