That is explained in the article. The second Lord of Baltimore combined the Calvert and Crosslands crests, and used that crest to make official documents, such as the map you linked to. However, it was never a flag. During the Revolutionary War, the crest was abandoned. During the Civil War, the crest was split, with the unionist Marylanders taking the Black and Yellow portion and using it as a flag, and the confederates taking the red and white portion and using it as their flag. 15 years after the war, the two parts were brought back together in the flag you see today.

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    Benjamin YoungSavage

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    • Independent Abolitionist • Graphic/Artist/Designer • Raised Native/Interracial Family/MK • Father/Friend • founded Zerflin • 🇺🇸🇨🇦 • 🇵🇱🇮🇪