Robin, I think that's a simplified schematic as the positioning of NRVs was discussed earlier in this thread by those with knowledge of type. There have to be flex couplings if solid pipes are used and bulkhead mounts, so I think we can assume a lot has been left out of the schematic for clarity.
However, the truth is that this accident was unexpected (aren't all?). We have an experienced and well-respected pilot and a major operator with a good safety record, crewed/manned by responsible people rather than a couple of champagne Charlies or "A-Listers" in the back making whoopee. The weather was excellent, viz good. This accident was never meant to happen so we can expect the unexpected.