As I recall, it was the "made the decision" bit which was critical -
there were people who had bailed out below 500m, but they had all made
the decision to do so while higher. However, I'd welcome correction
or, better still, a copy of the report. Anyone?

I recall my instructor telling me about a guy who got winched with
disconnected controls (or maybe they jammed during the launch?). By
the time he got to the top of the launch he was unstrapped and the
canopy was gone. He jumped and survived. The decision to jump was
obviously made well below 500m.

Bartek