El Pluscuamperfecto progresivo de subjuntivo

Pluperfect / Past Perfect progressive subjunctive

There is a progressive form of the pluperfect subjunctive tense called El Pluscuamperfecto progresivo de subjuntivo. It often expresses actions that hypothetically might have [not] been taking place in the past. 

 

Yo no creo que ellos hubieran/hubiesen estado trabajando en esas circunstancias.

I don't think they would have been working under those circumstances.

Thinking...