I would find it difficult to believe that the HSE after investigating MB and "finding a smoking gun" did not require MB to inform their customers, or indeed inform the customers themselves.
Customers were informed by MB Special Information Leaflet No. 704 in November 2011 and 704A in November 2013. Seeing as the accident happened on 8th November 2011 it is clear that the cause of the accident was known about, almost immediately.
DV