Sorry I forgot to link to their address finder: https://www.royalmail.com/find-a-postcode
The Irvine postcode is KA11 4DF and the Kilmarnock one is KA1 2FE - however on the RM site both are shown as the same place in Irvine on their map, so it must be their problem!

Only thing we can really do in OpenStreetMap is add the correct address data to each building. Can you confirm that this building: https://www.openstreetmap.org/way/1188370777 is number 1 Gleneagles Place and it goes clockwise from there to number 9 here? https://www.openstreetmap.org/way/1188370779