From the Preface of the linked PDF: This is version 2.1 of the document describing the RISC-V user-level architecture. Note the frozen user-level ISA base and

From the Preface of the linked PDF: This is version 2.1 of the document describing the RISC-V user-level architecture. Note the frozen user-level ISA base and extensions IMAFDQ version 2.0 have not changed from the previous version of this document, but some specification holes have been fixed and the documentation has been improved. Some changes have been made to the software conventions.