The solution indicated by the wordplay in each of the 26 clues is lacking a required letter. Each letter of the alphabet is missing from a particular clue, though in three cases it is missing twice and in one case three times.
1. There is surely some ambiguity here. In the first sentence Soup says that a letter is missing from each solution yet in the second that the letter(s) is (are) missing from
a particular clue. If it is the latter then it would be possible that wordplay may result in a single letter (eg in 7, 8, 20, 21).
2. There are twenty-six clues but we have 4ac and 4d. What does the setter mean by
Each letter of the alphabet is missing from a particular clue?
I may wait for confirmation.