The site was recorded for decades under the general category of "Enclosures" in successive national surveys, but work on the Iveragh Peninsula eventually produced a more precise identification: these are fionnán enclosures, a classification that sets them apart from the broader archaeological category they had long been lumped into.

Fionnán is the Irish word for a particular coarse grass, Molinia caerulea, sometimes called purple moor grass, which tends to colonise and mark out low earthwork features in wet upland terrain. When surveyors working on the Iveragh Peninsula, the broad finger of land in south-west Kerry that includes the Ring of Kerry, examined the Derrynagree site in detail, they concluded that what had been mapped as a conventional enclosure was in fact defined and preserved largely through this kind of vegetation patterning. The reclassification appears in O'Sullivan and Sheehan's 1996 survey of the peninsula, where the site is listed as entry number 38. That survey represented a substantial reassessment of the archaeological landscape of Iveragh, and Derrynagree was one of a number of sites whose official designation shifted as a result of closer fieldwork.