The video lens is coded to display a maximum of 100 results in its searches of local files. If there is no search terms entered, then it will display the first 100 local videos it finds. With search terms, it will display the first 100 videos matching the search terms that it finds.
The maximum limit is there for reasons of performance. It is also more difficult for users to find what they are looking for large numbers of results rather than try to reduce the number of results by using more specific search terms.
That being said, to increase the maximum number of results being displayed:
In a terminal, enter the following to edit the source code of the video lens:
sudo gedit /usr/lib/unity-lens-video/unity-lens-video
You will need to enter your password to edit this file.
In the file, find line 220:
if video_counter < 100:
(or press CTRL+F and search for 100)
Change 100 to a larger number ( e.g. 500) and save the file
Log out and log back in again. The video lens should now display a larger number of local files.