How to avoid duplicates when creating recent network posts

SOLUTION:

I added

$titles = array(); 

at the top (outside the loop).

Then, within the loop, I used

array_push( $titles, get_the_title( $ID ) ); 

to collect the titles.

Then I just checked the array for a matching title before displaying, like this:

if ( !in_array(get_the_title( $ID ), $titles ) )
    ...then do this

And it works!