1. "When I started a few years ago, he was already working there. " = Correct - - - y - - - z If 'z' is the present time, and 'y' is point in the past when you joined the company, - - - - - is the ongoing situation AT that time: "he was working there". 2. "When I started a few years ago, he’d already been working there." = incomplete "When I started a few years ago, he’d already been working there for six months" = correct x - - - - ->y z Here, 'z' is the present, 'y' is the point when you joined the company (a few years ago e.g. June 2015) and 'x' is the point when Joe joined the company six months PREVIOUS to that (e.g. January 2015). - - - -> is the time BEFORE 'y': it's the period of six months leading up to the point when you joined the company = 'he had already been working there for six months'. I hope that makes sense.