In a post last year (Ordnance Survey Data Importer Coordinate Conversion Accuracy) I looked into an accuracy issue with the conversion process within the GeoCoordConversion DLL that I use in this project (blog post). Bottom line, was that it was a minor with an average inaccuracy of around 2.5 metres and a max of ~130 metres by my reckoning. I’ve since had a few requests asking if I can supply an updated GeoCoordConversion DLL with fixes to the calculations.
After getting in contact with the owner of the GeoCoordConversion project, they’ve kindly added me as a committer. I’ve now pushed the fixes up to it, rebuilt the DLL (now v18.104.22.168) and pushed up the latest DLL to the Ordnance Survey Importer project on GitHub.