The 804 right backs weren't scouted but were plucked from a database according to reports.
The issue was that the scouting heads and Solskjaer and Phelan weren't on the the same page. And the strategy was to sign British players that summer, so the 804 right backs were narrowed down considerably due to the criteria set by Solskjaer and Phelan imo.
The below snippet from the Daily telegraph is just one of a number of reports which mentions Wan Bissaka being selected from a database.
Daily telegraph: "Before signing Aaron Wan-Bissaka from Crystal Palace, Manchester United started out with a database of 804 right-backs. They wanted a young player, preferably British, and, given the way that manager Ole Gunnar Solskjaer wanted his defence to push up, one that was also very good at so-called ‘recovery runs’ - getting back into position when possession was lost, something of a specialism for Wan-Bissaka"
https://www.telegraph.co.uk/football/2019/10/15/manchester-united-have-method-madness-dont-talk/