I found this one frustrating: I think I have it all, but in order to find one missing pair of letters I was reduced to searching the text of the clues in Word. The trouble with two letter, for the most part real, words is that their presence in a clue can be highly ambiguous. The word "is" for example, could be seen as superfluous in several clues, even though it may not be one of the pairs we're looking for (see how I strain not to "give anything away"!). Oh well.