User blog comment:B214/Volume 22 spoilers/@comment-202.67.40.227-20161030103910/@comment-10330822-20161030143037

I don't feel its a useless question. Think of it like this. Say you are a member of British society. You are very wealth and are considered a "high-class" individual. Now, that doesn't technically mean you are also a noble. You have to be given a title to be a noble. To our knowledge, or at least mine, the only devils with titles, are the members of the 72 pillars. That being said, because Issei is high-class, he would be qualified to receive a title, or, marry into a family with one. Issei could be made something, but it doesn't really matter, because if he marries Rias, he'd just be a Duke anyway.

In terms of class status, higher classes mean you have larger "territories", Ultimate-Class Devils are given their own territory to rule. Does that mean they have a title, don't really know.