It's a bit difficult to say from what time exactly Nomos went to in-house movements, but I would say a comparable situation as Bremont has now - where they are using a foreign IP and are adding some improvements to it - was reached by Nomos already in 1993, about one year after they introduced their first watches to the market. In 2004 and 2005 they introduced their in-house designed movements (manual and automatic) and from 2014 they introduced the DUW movements with the Nomos-Swing-System.
This document (in German) describes the development from the Peseux movement to their in-house calibres.