Thinking about it from my dialect, I do think there is a stronger voicing on the "s" in "scent" and "cent" but not the "s" in "sent" (might even be as distinct

Thinking about it from my dialect, I do think there is a stronger voicing on the "s" in "scent" and "cent" but not the "s" in "sent" (might even be as distinct as /s/ versus /z/? But probably with a partial-voiced marker on one or the other?). Also, I think "cent" is the only one where the vowel seems always forced, not schwa-ed /ə/. It's not always the case, but there can be a reason to believe that spelling differences may have arisen in such cases from trying to explain subtle distinctions that mattered to someone's dialect before a lot of the modern work went into the IPA and actually capturing those subtle differences.