Should they be classified as data CDs if they don’t have an Enhanced CD certification mark?
I tend to mark any CDs that have data on them as Enhanced CD. I’m not sure if that is technically correct or not but there is no generic “audio + data” type available and I definitely have a few audio CDs that have data on them that are not marked as “Enhanced CD” or any of the other variations listed on the wikipedia page.
Depending on the format/platform of the disc, I might not use any form of CD at all. Maybe “Other” and an explanation of what format the disc is (e.g. a PlayStation game disc).