Well its true it is a small world after all.
I had a phone call from a watchmaker friend in Finland this morning. It turns out he was the watchmaker who worked on the 16710 in the thread. He confirmed it was definatley a 3186.
I guess that any 16710 cases left without movements when production of the 3185 ceased had 3186 movements fitted.
Guess they`d be pretty rare.