I once tried to count the changes in speed limit on the Waterford - Carlow - Dublin route not including towns and villages and got up to 26 before giving up. Some of them are marked by a single little lollipop that can be obscured by a truck on the inside lane.
The NRA is responsible, if you want to give out to someone. If you look closely, there is usually a good reason for the slower sections - junctions, lights or whatever. It is the fault of the inconsistency of the road quality, rather than the signage.