lost my font in the epub

[rapunza]

Hello again, community. I've got an ebook that I've been perfecting with Calibre. Up until now the file has correctly displayed its fonts when I view it with ADE.
PROBLEM: Then, a few days ago the Crimson Text just disappeared, leaving Times New Roman in its place since that's the secondary serif font in the CSS. As far as I can tell, I didn't make any font changes that could have caused this; I've only been making text changes to the book's HTML pages. Also, I don't include style code in the HTML pages, just in the style sheet.
ATTEMPTED SOLUTION: I have a backup version of the file that shows Crimson properly. Today I tried copying the CSS file of that backup to the current file, but that didn't solve the problem.
QUESTION: Does anyone have any ideas of what I can try next? (I'm reluctant to just go with the last Crimson-showing file, since I made a bunch of tricky-to-replicate text changes since then—and in case the problem just returns.) Thank you!