With the help of this forum I'm a long way down the road, but I am still struggling to make sense of the rubric as far as the additional letters are concerned. After 214 posts I assume that I can discuss an actual answer, so let's look at the Bugloss clue as a case in point. Definition = bugloss, wordplay = bled (exuded sap) + ewe, answer = blueweed. Now, in what way does this conform to either "letters are ignored in their clues' wordplay" or "the wordplay gives an extra letter that is not entered"? I assume the latter is the relevant case, but it seems to me that - far from the wordplay giving an extra letter that is then omitted from the grid - the wordplay needs an extra letter to be added before entry in the grid.
I expect this is me, but I'd be very grateful if someone could explain to me how this clue works in the light of the rubric.