Hey JayBee,

Thank you for contributing to OpenStreetMap.

Local knowledge is a valid source for OpenStreetMap, but regardless I have checked the information you provided.

On historical maps, the label does point more clearly to the adjacent building in the 25 inch (which we can use only for reference, not for mapping, as it is still copyrighted and otherwise not explicitly permitted for use by National Library of Scotland.

However, the NIAH/NBHS building inventory
https://www.buildingsofireland.ie/buildings-search/building/12401306/clomantagh-lower-clomantagh-kilkenny
does mention it was in use as RIC barracks.
(maybe it counts adjacent building as part of it)

but a discussion on a blog post article which you may or may not be aware of, which includes (family of) owner, mentions similar idea as you do, where it was barely in use as RIC barracks (but due to rumors people assumed it was built as or always used as such).
https://theirishaesthete.com/2016/12/14/an-architectural-conundrum-update/

Resolved in
https://www.openstreetmap.org/changeset/169609975

Changes visualised
https://overpass-api.de/achavi/?changeset=169609975

Sidenote: Changed name to description, since this seems to be case of descriptive name
https://wiki.openstreetmap.org/wiki/Names#Names_are_not_for_descriptions
in Ireland users tend to use the name tag anyways, but usually it should be only done where it was the common name. (due to being solely outbuilding I assume it's not the case)