User blog comment:B214/Volume 23 discussion blog/@comment-77.188.244.97-20170428163113/@comment-29963364-20170428200139

The servants of Rias, Sona, Sairaorg, and Sirzechs (and possibly Rizer) are actually rare cases among the servants of most other Devils who have peerages.

During the Giant Monster attacks in vol.12, Reincarnated Devils and servants were rioting during the chaos, trying to escape their masters. This proves that not all servants aren't treated nearly as nicely, or given the freedom that Issei and the other servants we've seen.

Take Diodora Astaroth for example. He tricked and turned his servants, who were former nuns & holy maidens, into his "slaves." But I know that Diodora is an "extreme example", so he's not the best example to compare other Devils to. But it still gives some indication of how Reincarnated Devils and servants are treated.

And remember Zekram from vol.18? He says "reincarnated ones" (Reincarnated Devils) and "servants" (Commoner Devils). He doesn't even consider Mid/Low-Class Devils as "Devils" at all, whether they're Reincarnated or Pure-Blooded.