The Mathematics Subject Classification (MSC2010) is the previous version of the MSC2020. It has been used by Mathematical Reviews (MR) and Zentralblatt für Mathematik (Zbl) since 2010. There has been a previous version of MSC2010 as well, the MSC2000.
"The Mathematics Subject Classification (MSC) underwent a general revision, with some additions and changes, and corrections of existing errors, thus creating MSC2010 as a successor to the previous MSC2000. Mathematical Reviews (MR) and Zentralblatt für Mathematik (Zbl) carefully considered all feedback and used it in preparing their joint MSC revision.
The Final MSC2010 revision was made public here [http://msc2010.org/Default.html] in May 2009, and deployed in production in July 2009 by MR for MathSciNet and Zbl for zbMATH."