Before 2021, files like mkl_rt.dll and mkl_core.dll were standard. Starting with , primary DLLs were renamed to include version numbers—such as mkl_rt.1.dll and mkl_core.1.dll —to allow multiple versions of the library to coexist on the same system without conflict. Intel® oneAPI Base Toolkit Release Notes
prefix refers to the various shared objects (on Linux) or DLLs (on Windows) that make up the library. Key files often mentioned in 2021 developer discussions include: Intel MKL FATAL ERROR libmkl · Issue #2937 - GitHub libmklccgdll 2021