CURRENTLY YOU HAVE YOU HAVE YOU HAVE YOU HAVE
end | has_top_lists | has_download_top_list
10  | 1             | 1
20  | 0             | 1

But lets say person 1 downloaded that top_list project only AFTER sharing
the fifth project and person 2 downloaded after 15...

You want...
(experiences event at end!) 

start | end | has_top_lists | has_download_top_list
1     | 5   | 0             | 0
5     | 10  | 1             | 1
1     | 15  | 0             | 0
15    | 20  | 0             | 1