Hi Jeremy,
I wasn't suggesting that they were placed over bodkins at all - as far as I'm aware (and looking at the blunts Mark made) it's all wood. The blunt itself (the main body bound with natural fibres and turned) is wooden, as is the sharp point sticking out. Whether it's all a single piece or not I don't know, but it makes more sense if it is one piece.
My own personal interpretation of it all is that steel was saved for the military heads due to cost and labour (both in preparing the steel and in forging the heads) and most other types of head used for practice, hunting, sport etc would be wooden, keeping the cost down and ergo resulting in far fewer metal heads being found in areas that weren't involved in battle.
So to clarify, I don't think the blunts were placed over bodkins, but that the blunts included sharp wooden spikes at the end, either turned with the blunt itself or fixed somehow to the blunt. Perhaps even the arrow shaft itself was sharpened and heated to strengthen it, and a blunt placed around it to provide the necessary weight?
When Mark and Ian write up the next bit hopefully they'll discuss his methods of construction.