Bebbspoke, 19a has an extra letter in mousey.
19d. Islanders is the definition.
20d. Has a missing letter in dad.
Not sure what you mean by two separate occurences for the fourth work. It has 5 letters in a row.
Thanks cloverjo - the two "separate occurrences" are 3 consecutive letters in a row, and 4 consecutive letters in the next row... there is possibly another 3 letter example in the next row too - but this conflicts with one of the more obvious (6 letter) works?...
cloverjo - surely the 3 letters to which we refer are letters 2,3 & 4 of a 6 letter answer to a work of 1922, similar to another 6 letter work, a decade later as implied two rows further down... or am I being too obtuse?
Bebbspoke, I don't think the latter two you mentioned are the ones we're meant to highlight. There are certainly four works represented in the grid that don't include those two.