Type 19s are end-of-terrace flats. They appear in the blocks which face north and south, with flats running from front to back. They are cousins to the Type 20 and Type 21 flats which slot together round the stairwell of the block. The Type 20 flat then takes the remaining bit between the stairwell and the front of the building as extra living room or 'study' and the Type 21 takes the remaining bit between the stairwell and the back of the building as an extra bedroom. The Type 19 has the best of both worlds - with no-one to share with - being at the end - it takes both bits and walks away with 2 bedrooms, a living room and a study (4 rooms). There are 12 in Andrewes House, 12 in Thomas More House, and 6 in Speed House. (in other words 1 per floor for 6 floors, at either end of each house, except Speed House where they are at only one end - I don't know which).
