Three of the even number households look to be indexed just under "Leslie", but 16 isn't one of them.
If you do a name search for those under a road name "Les" within Thornton Cleveley, 51 (open) names appear (including the Cleggs). When this extends to "Lesl" that drops to 30 (excluding the Cleggs), so they are not alone in being "elusive". This drops further to 27 when you further extend to "Lesley A", so the three addresses indexed just as "Lesley" would seem to contain three open people (one contains 2 open, another contains 1 and the third none - there are varying numbers of closed individuals).
I have tried to get the fourth character, but without success. Either I missed a letter when going through, or it is not one of the 26 letters, but something else - number symbol, etc). I'm guessing when you can work out that fourth character, you'll find those "missing" 21.