  The discovery of a kilonova associated with the GW170817 binary neutron star
merger had far-reaching implications for our understanding of several open
questions in physics and astrophysics. Unfortunately, since then, only one
robust binary neutron star merger was detected through gravitational waves,
GW190425, and no electromagnetic counterpart was identified for it. We analyze
all reported electromagnetic followup observations of GW190425 and find that
while the gravitational-wave localization uncertainty was large, most of the
90% probability region could have been covered within hours had the search been
coordinated. Instead, more than 5 days after the merger, the uncoordinated
search covered only 50% of the probability, with some areas observed over 100
times, and some never observed. We further show that, according to some models,
it would have been possible to detect the GW190425 kilonova, despite the larger
distance and higher component masses compared to GW170817. These results
emphasize the importance of coordinating followup of gravitational-wave events,
not only to avoid missing future kilonovae, but also to discover them early.
Such coordination, which is especially important given the rarity of these
events, can be achieved with the Treasure Map, a tool developed specifically
for this purpose.
