Is there a way to sort backups listed in Rom Manager?
EDIT: Nevermind. Turns out the Rom Manager installation on CM9 wasn't actually up to date, and apparently my backups were not all named consistently. It seems that Rom Manager uses the format:

YYYY-MM-DD-HH.nn.ss

while CWM Recovery uses the format:

YYYY-MM-DD.HH.nn.ss

which is why they didn't seem to sort correctly. Updating and making the names consistent solved the issue.