That was very tough. Had to guess 19 and relieved to see from the posts here I was right, would never have got that.
Not sure anyone has answered S Pugh from way back at post 20? I think the reason the setter didn't put any words in columns 2/11 is that if the did they would have created words with no unches - all of the across answers on the left from 25 to 43 (incl 42) have col 2 as their only unch. For many purists words with no unches are undesirable, partly because you can finish the crossword without solving every clue. When you submit a crossword the editors check 'overunching' and 'underunching'.