USO: Para enfatizar la diferencia temporal entre dos estados, acciones o hechos en el pasado que se mencionan en la misma oración. Por lo general usamos el Pasado Perfecto si queremos enfatizar que un hecho o astado acontecio antes que otro.
'I was really suprised when I met Sarah at Dave's party last month. I hadn't seen her for 10 years, and she looked really different. I asked her what she'd been doing since we finished university, but she didn't tell me. Then somebody told me she'd been working as a stripper'
USO: Para enfatizar que un hecho acontecio antes que otro (conectado mediante conjunciones como WHEN y BEFORE) o en el modo indirecto, cuando el "verbo informante" esta en pasado y la afirmación o idea "origional" estaba en Pasado, Presente Perfecto o Pasado Perfecto.
[SUJETO + HAD (+ Adverbio) HAD NOT/HADN'T + PARTICIPIO PASADO...]
'He had just arrived when she appeared.'
'We had already finished by the time they appeared.'
'The match had just begun when we parked the car.'
'I had never been angry until I met her!'
[PASADO + (THAT) + PASADO PERFECTO]
'I thought (that) you'd already been here.'
'He said (that) he'd never seen me before.'
USO: Para hablar sobre acciones o estados continuos que acontecieron hasta un cierto momento en el pasado.
[SUJETO + HAD/HAD NOT (HADN'T) + BEEN + VERBO + ING...]
'I'd been waiting for 30 minutes when she arrived.'
'He hadn't been working much until he lost his first job.'
'They'd been waiting for 70 minutes when he scored the first goal.'