This is actually really common for smaller ones: 2015: https://en.wikipedia.org/wiki/List_of_asteroid_close_approaches_to_Earth_in_2015 https://en.wikipedia.or

This is actually really common for smaller ones: 2015: https://en.wikipedia.org/wiki/List_of_asteroid_close_approaches_to_Earth_in_2015 https://en.wikipedia.org/wiki/List_of_asteroid_close_approac... 2016: https://en.wikipedia.org/wiki/List_of_asteroid_close_approaches_to_Earth_in_2016 https://en.wikipedia.org/wiki/List_of_asteroid_close_approac... 2017: https://en.wikipedia.org/wiki/List_of_asteroid_close_approaches_to_Earth_in_2017 https://en.wikipedia.org/wiki/List_of_asteroid_close_approac... 2018: https://en.wikipedia.org/wiki/List_of_asteroid_close_approaches_to_Earth_in_2018 https://en.wikipedia.org/wiki/List_of_asteroid_close_approac... All the ones coloured red in the tables (the majority) weren't discovered until after their closest approach.