jeffb, old/obsolete aircraft relegated to the training role certainly contributed their own problems. The Blenheim was state of the art in its day no doubt but that was many years, let alone days, in the past. As a Bomber OTU stalwart its shortcomings may be gleaned by the many RAF war graves in Oxfordshire churchyards alone. Perhaps it was your father's good fortune that it does not feature in your list and hence, presumably, in his log book.
Of the 55573 aircrew losses remembered by the Bomber Command Memorial, over 8000 are ascribed to training losses I believe. Of course many of those would be due to aircrew error and lack of experience rather than aircraft shortcomings, but the latter has a habit of encouraging the former...