This is not correct, the nature of gravitational waves emitted by the merging of two objects is different in its final stage, depending whether the objects form a black hole or not. Until a black hole is formed, the nature of the emission is the same for all objects (e.g. black holes or neutron stars), but if a black hole forms, the final emission (ringdown) is different.
The first LIGO-Virgo events detected black hole mergers which resulted in black holes.
The last LIGO-Virgo event detected two neutron star mergers. Unfortunately the sensitivity of the apparatus is not good enough to determine if the merge resulted in a black hole, or a neutron star based purely on gravitational wave measurements. However, we have secondary evidence[1] that the remnant was a black hole.
The first LIGO-Virgo events detected black hole mergers which resulted in black holes.
The last LIGO-Virgo event detected two neutron star mergers. Unfortunately the sensitivity of the apparatus is not good enough to determine if the merge resulted in a black hole, or a neutron star based purely on gravitational wave measurements. However, we have secondary evidence[1] that the remnant was a black hole.
[1] https://arxiv.org/abs/1710.05938