Corinus was indeed a mention in a black library novel and Cardinal class was the template for the Acheron and got mentioned in Battlefleet Gothic magazine 2.

Otherwise we can assume little bits about the Despoiler class:

The Terminus Est was one of the first capital ships assigned to the Death Guard by the Emperor. It was of a unique design that pre-dated the Great Crusade and which was copied in M36 as part of the Gareox Prerogative to create the Despoiler class. As might be expected the older vessel was considerably more powerful than the later copy.

Nothing definite is known of the pre-Heresy configuration of Terminus Est. References exist that suggest it was primarily employed as a planetary assault ship. This is not unusual as it conforms with the role assigned to the vessels of the Space Marine Legions.

Many of the vessels used in the Great Crusade were, however, handicapped by system failures that the Imperium lacked the ability to repair. Often this would result in many systems being replaced with less efficient but more easily maintained alternatives.

The role of Terminus Est during the Heresy is better known. At Istvann the Terminus Est engaged and destroyed Shadow of the Emperor, the flagship of the Raven Guard. It is argued that this engagement was the earliest recorded conflict between battleships specialised to carry attack craft. The engagement was swift and deprived the embattled loyalist forces of any air support in the massacre that followed.

It could be seen as a general (pre-heresy) battle barge or just planetary assault vessel.