Dreyer published two supplements to the NGC in 1895 and 1908, known as the Index Catalogues (abbreviated IC), describing a further 5,386 astronomical objects.

Objects south of the celestial equator are catalogued somewhat less thoroughly, but many were included based on observation by John Herschel or James Dunlop.

The NGC contained multiple errors, but attempts to eliminate them were made by the Revised New General Catalogue (RNGC) by Jack W. Sulentic and William G. Tifft in 1973, NGC2000.0 by Roger W. Sinnott in 1988, and the NGC/IC Project in 1993.

Dreyer had already published a supplement to Herschel's General Catalogue of Nebulae and Clusters (GC),[2] containing about 1,000 new objects.

In 1886, he suggested building a second supplement to the General Catalogue, but the Royal Astronomical Society asked Dreyer to compile a new version instead.

[3][4] Assembling the NGC was a challenge, as Dreyer had to deal with many contradictory and unclear reports made with a variety of telescopes with apertures ranging from 2 to 72 inches.

[8] The Revised New Catalogue of Nonstellar Astronomical Objects (abbreviated as RNGC) was compiled by Sulentic and Tifft in the early 1970s, and was published in 1973, as an update to the NGC.

Dreyer corrected his own mistake in the Index Catalogues, but the RNGC preserved the original error, and additionally reversed the sign of the declination, resulting in NGC 2163 being classified as non-existent.