  We point out that past-incompleteness of geodesics in FLRW spacetimes does
not necessarily imply that these spacetimes start from a singularity. Namely,
if a test particle that follows such a trajectory has a non-vanishing velocity,
its energy was super-Planckian at some time in the past if it kept following
that geodesic. That indicates a breakdown of the particle's description, which
is why we should not consider those trajectories for the definition of an
initial singularity. When one only considers test particles that do not have
this breakdown of their trajectory, it turns out that the only singular FLRW
spacetimes are the ones that have a scale parameter that vanishes at some
initial time.
