Can see your post now, Brendan (and others above). I put 20 across in the category defined by the extra word in 28 across, though from the Wiki entry it doesn't seem quite right.
my post 46 (of 45 now - before it was 42!) is irrelevant as everyone has crossed as a result of delayed publication (which happened to me on page 2 yesterday). Yes, I too believe the extra word in 28 goes with 4d.