The quality of the datasets varies greatly depending on the source. Some work well, some, less so. There are data sources that are undergoing active development to harvest them more accurately. None of them were added to pump up the numbers.

The biggest numbers bump recently was ca 1600 Met Eireann rainfall records datasets from all around the country, some of them daily rainfall dating back 60 years. (Spoiler, there’s a lot of rain)

This is specifically a catalog of data sets, it doesn’t host the data except for previews, and even doing that is pretty complicated in all its glory.