Oddly enough an post addresses and GeoDirectory don't have any legal standing. Many of the ones I checked were wrong. They seem just to accept what people tell them. DEDs don't have any relationship with natural boundaries or specific townlands. But they group townlands together. So if you're happy to ignore the townlands, then you have to accept Coolmine, Delwood, and all those other places all over D.15 can call themselves Castleknock if they feel like it aswell. Which exactly what they do.
Which is why most people don't believe anyone when they give an address in D.15. its become meaningless.
An Post lists (using Geo directory)
- Delwood as Blanchardstown,
- Riverwood as Carpenterstown,
- Roselawn as Blanchardstown
- Brompton as Blanchardstown
[broken link removed]
Try it before you say it doesn't work.
The DED is pretty accurate as to what is Blanchardstown and what is Castleknock.
In fairness people should not be going to these lengths to determine where a property lies particularly if its inclusion in a better area means it attracts a higher price.