Same Events, Weaker Bound: Model Dependence in Magellanic Microlensing Limits on Primordial Black Holes

OGLE microlensing of the Magellanic Clouds sets the leading bounds on primordial black holes (PBHs) as dark matter from ${10}^{-8}$ to ${10}^3{M}_{\odot }$. Holding the detected events and survey efficiencies fixed, we show that changes to the Milky Way halo, the stellar lens populations and the Large Magellanic Cloud halo, each motivated by recent data, weaken the published strict 20-year bound by up to $\simeq 6$, and by over an order of magnitude in an extreme stress test. With primordial clustering, the planetary-mass bound weakens by a factor $3.4$–$6$. We strongly recommend that compact-object dark matter limits be quoted together with their modeling assumptions and, generally, be derived under conservative assumptions.