I would read that as the “number of bankcard accounts never delinquent” is insufficent. Meaning there aren’t enough good accounts. Most or all of your accounts have been delinquent. I’m just parsing words though, only you and the credit company know about your accounts.
Agree with shiftless, though it could also just mean you don’t have enough accounts, even if the ones you have were never late. So someone with only 2 perfect accounts, and someone with 10 accounts, 8 of which had been delinquent at one time or another, would get that same comment.