"I was joining and other aircraft had just joined and when i was overhead i called G-aaaa can i have your position please because i had not heard him call downwind ".
How then, did you know that he had just joined?
If you were in the overhead, about to descend deadside, why call him at all? There was no conflict. A blind position report would have told him what you were up to. That's why we make such calls.