O-2 - Neutron stars with ages of 100 Myr to Gyr are observed intact
Secondary anchor bodies (density ~10^14 g/cm^3 stops any TeV black hole); the NS bound needs extra assumptions about cosmic rays penetrating NS magnetospheres, so G-M treat white dwarfs as the more robust case.
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Why this is evidence
H-1 predicts cosmic-ray-produced stable black holes stopped in neutron stars would have consumed them within 10^8-10^9 yr; H-2 predicts survival. Intact old neutron stars are surprising under H-1, expected under H-2 (modulo magnetosphere-penetration assumptions).