A better way to think about it is that all letters in the musical alphabet are represented in a musical scale. Some are sharp or flat
D major: D E F♯ G A B C♯
D minor: D E F G A B♭ C
Db major: D♭ E♭ F G♭ A♭ B♭ C
Db minor: D♭ E♭ F♭ G♭ A♭ B♭♭ C♭
D major: D E F♯ G A B C♯
D minor: D E F G A B♭ C
Db major: D♭ E♭ F G♭ A♭ B♭ C
Db minor: D♭ E♭ F♭ G♭ A♭ B♭♭ C♭
My point was not to showcase my confusion, rather to reinforce the fact that music theory texts are just generally low quality, and music theory as a field seems to be okay with that.