There are the following sentences:
- "I had been waiting for three months before they finally sent me an answer"
- "He had been waiting for the bus for 10 minutes before it arrived"
Does "before" essentially mean "when" in these sentences? I think this is why the past perfect continuous is used in them.
There are other sentences which have "before" in them and that aren't in the past perfect continuous tense. For example:
- "Marilyn was a factory worker before she was a model"
- "They were married for 10 years before they got divorced"
- "I was dissembling before you were born"
Am I right in thinking that the past perfect continuous is needed when "before" means "when" (in the meaning "by the time")?