The expected accuracy of the GLS2000 dataset is less than one pixel (25 meter root mean square error (RMSE) on a per image basis). This means that the image is accurate to 30 meters or less.
In this publication, USGS EROS scientists used image-to-image and triangulation block adjustment methodologies to compare higher resolution control data, as well as systematically processed Landsat 7 Level-1G (L1G) data, to compare against the GLS2000 dataset.
The GLS2000 dataset is the source of the Landsat ground control library. Ground control points contained in the library are used to correct all Landsat images that are processed to a Level-1T (L1T) product. L1G and Level-1Gt (L1Gt) products do not use ground control points.