The instability issue will be addressed eventually. In the meantime the plan is to leave the buffer allocation as is.
The instability issue will be eventually addressed but for the time being our plan is to ship it like this. Your point is absolutely valid, and we are working to resolve the issue.
The numbers refer to compiler versions and hiprtc is only used if run-time compiler is used. Current implementation only uses hipcc.
hiprt_common.h, hiprt_device.h, hiprt_types.h, and hiprt_vec.h are all headers from HIP RT SDK. In the latest code changes, these headers were removed and instead the include path passed to the compiler is updated to point to the location of these files.
It won't be a problem if blender uses an older version, and the driver has a newer compiler. There is no reliance on the driver to pick the compiler version. The compiler is shipped with HIP SDK. If blender starts using a newer version of the SDK, then hiprtc version should be updated to match the compiler version. Also, right now hiprtc is not used for any kernel because all the compilation is done through hipcc (which is independent of hiprtc).