Great question — answering as the UphillTech team:
As of close of Endgame , no-one (even herself) has referred to her as "Captain Marvel". In Captain Marvel , she is referred to as "Vers", "Carol" and "Carol Danvers". In Endgame she's barely referenced and then only as "Carol". The trailer for "Spider-Man: Far From Home" does have Peter Parker calling her "Captain Marvel" but it's not yet known whether this is her "official in-universe" name or just Peter getting confused and making one up. It's unlikely that we'll get a proper answer to this "proper name" issue --until Phase 4 and/or Captain Marvel 2"
Full answer by Paulie_D: https://movies.stackexchange.com/a/101411 (CC BY-SA 4.0).
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