And may I add to Sue's thoughts ...
At Line 1, it seems someone has written in pencil so that the person with the ink pen can write over it, particularly Glen in column 1, and Head in column 2.
The handwriting at 686 is similar hand to 682.
The handwriting in pencil at 687 is likely from the enumerator, it is similar to 683, 685, 689 etc. It is NOT matching up to the even numbered images which of course are for the householder to compete.

so I think Mr Fitzgerald at 18/2 Burlington St has helped 18/6 fill out their forms, there's only Mr Flannery at 18/4 separating them.
JM