Notes on verification

Multiple independent English and French sources (Guinness World Records, Wikipedia, Britannica, Grace's Guide, French aviation history sites) corroborate the date, location, and circumstances of Lefebvre's death, with no contradicting sources found. [cascade flags: aggregator_dropped_primary_exists,wikipedia_dropped_other_sources_exist | tier=bronze indep_score=0.546 clusters=5 claim_tier=notable | framework convergence=partial (upstreams: Bibliothèque nationale de France (BnF) authority records, contemporary New York Times reporting) — publishers independent, evidence may not be | kind=empirical eligibility=high]