As of 2018 NIST does not provide certificates for the common stable isotope reference materials. As seen at this [https://www-s.nist.gov/srmors/viewTableV.cfm?tableid=42 link] showing the light stable isotope references currently available from NIST, this category includes all of the isotopic references critical for isotopic measurement of hydrogen, carbon, oxygen, nitrogen, and sulfur. However, for most of these materials NIST does provide a report of investigation, which gives a reference value that is not certified (following the definitions of May et al. (2000)). For the above examples of USGS34 and USGS35, NIST reports reference values but has not certified the results of Böhlke et al. (2003). Conversely, NIST has not provided a reference value for IAEA-SO-5. As seen at this [https://www-s.nist.gov/srmors/viewTable.cfm?tableid=41 link], NIST does certify isotopic reference materials for non-traditional "heavy" isotopic systems including rubidium, nickel, strontium, gallium, and thallium, as well as several isotopic systems that would normally be characterized at "light" but non-traditional such as magnesium and chlorine. While the isotopic composition of several of these materials were certified in the mid-1960s, other materials were certified as recently as 2011 (for example, [https://www-s.nist.gov/srmors/certificates/951a.pdf Boric Acid Isotopic Standard 951a]).