Stops.csv shows a list of platforms with their coordinates. They all have the same coordinate for every station. One way to update this information is to use Open Street Maps (for example: http://www.openstreetmap.org/#map=18/51.03557/3.71009). As you can see, there's no indication of the trainplatforms and I don't know if there are any APIs that provide this information...

So if you know which platform corresponds with a certain spot on the map, you can PR with better coordinates.