Present Perfect Continuous vs Past Perfect Continuous

The past perfect continuous corresponds to the present perfect continuous, but with reference to a time earlier than 'before now'. As with the present perfect continuous, we are more interested in the process.

 We use the Past Perfect Continuous to show that something started in the past and continued up until another time in the past. Notice that this is related to the Present Perfect Continuous; however, the duration does not continue until now, it stops before something else in the past.

She has been working at that company for three years. (she is still working)
She had been working at that company for three years. (she doesn't work there any more)