The uniform 19-digit code used for bibliographic references within NED and SIMBAD was developed by both teams in consultation with Dr. H. Abt, editor of the Astrophysical Journal.
The primary purpose of the REF_CODE is to provide a unique and traceable representation of a bibliographic reference within the structure of each database. However, in many cases, the code has sufficient information to be quickly deciphered by eye, and it is used frequently in the interfaces as a succinct abbreviation of a full bibliographic reference.
Since its inception, it has become a standard code not only for NED and SIMBAD, but --- with minor variations --- for ADS and other bibliographic services. In addition, the acronyms for journals used as part of the code have become standards for some of the main astronomical journals in their own bibliographies.