I’ve always being irked by OSM giving the wrong Postcode for some roads near my home area. Some roads give postcode 42000 but for some nearby it gives 41200.

Reading what Ionvia says enlightens …

• Nominatim has to go a different way to determine the most likely postcode for a place where no addr:postcode tag exists.
  • First - search address from specific up to country, use postcode for first found addr:postcode tag.
  • Second - area search, the closest postcode centroid is used

It turns out the roads in my area are almost exactly in between 42000 centroid and 41200 centroid as overlayed screenshot below shows …

Looks like long term solution to wrong postcode for my local area would be to tag Bandar Bukit Tinggi 2 with addr:postcode=41200 …