Why is the Mesa OpenGL driver for Intel chips called i965?

As I understand, most Intel GPUs are supported on Linux by two different components : i965 (the Mesa/OpenGL part, supporting all recent Intel GPUs) and i915 (kernel part, similarly supporting all recent Intel GPUs). The relationship between the two is not very clearly explained anywhere I found, especially now that names like iHD (for VAAPI), or Iris (newer chips) are mixed in, but essentially I understand that i965 uses features exposed from the kernel by i915 (syscalls/ioctls?) to expose the OpenGL API to applications. While https://unix.stackexchange.com/questions/224240/why-is-the-intel-hd-graphics-driver-called-i915 answers the question about the kernel part, why use a similar yet different product name for the Mesa component that supports all Intel GPUs anyway? Is there a reason behind it, or just history?