Heya. It looks like post box CA13 89 is already mapped at https://www.openstreetmap.org/node/3370196453. I assume you only just surveyed it as being on Fern Bank, so that suggests it’s been physically moved from Sullart Street at some point, or the original mapping was wrong.

If you could, it would be handy to survey the old location on Sullart Street and see what’s going on there.

If that’s not something you have time for, that’s fine; I can leave a note on the old location so someone else can check it out eventually.

There’s a map of postboxes here: https://osm.mathmos.net/postboxes/progress/CA/CA13/#11/54.6147/-3.3296

Hope you have a good day :)