More Chinese Character Troubles

While browsing through a Chinese character dictionary to see how one renders certain names, I came across the name "Dante Alighieri," which was written as 但丁 (Dàn dīng). I thought that perhaps this first character, which means "only; but, however, yet, still," could be the standard for "Dan." The Book Of Daniel uses the same character in 但以理書 (dàn yǐ lǐ shū), suggesting the first three might render Daniel.

Dan Brown, however, has a name written as 丹布朗 (Dān Bù lǎng), using the character 丹 (cinnabar, vermilion). This character is also used for several Den- names in English, Denver 丹佛 (Dān fó), Dennis 丹尼斯 (dān ní si), Denmark 丹麥 (dān mài).

These two characters (但, 丹) seem to be the most common to use for spelling Dan- and Den-, as they seem to be relatively common characters, with a variety of compounds already using them. But why is it that these names seem to split this way, and why is Dan Brown on the e side of this a/e split?

Actually, Mr. Brown isn't the only oddity I found, Tennyson also begins with 但, 但尼生 (Dàn ní shēng). It's probably not the case that there is a semantic meaning involved. It also doesn't look like there is a basis for which one is used by tones, or that much of a guideline based on the vowel sounds. From loanwords listed, 但 has [a, æ, ɛ] and 丹 has [æ, ɛ, ɛ, ɛ].

My best guess? Different standards over different periods of time, or different bodies or persons presiding over the first transliteration. Aside from Dan Brown, most of the other names have been around for some time, and it is likely that Chinese terms have existed for some time. Dan Brown is probably a relatively new innovation, which for some reason gets 丹 instead of 但. If anybody has any insights, let me know.