Error When pulling Triton Inference Server container version 19.10

I have installed Nvidia docker, and tried to pull the Triton Inference Server image by following the instruction from here [server/quickstart.md at main · triton-inference-server/server · GitHub].

I first logged in to my NGC account and received the message “Login Succeeded” in the console.
Then I ran the command docker pull nvcr.io/nvidia/tritonserver:19.10-py3,
And received the error message “Error response from daemon: manifest for nvcr.io/nvidia/tritonserver:19.09-py3 not found”.
I also tried pulling other container version of Triton Inference Server, like
docker pull nvcr.io/nvidia/tritonserver:20.07-py3 and docker pull nvcr.io/nvidia/tritonserver:20.08-py3, which both worked perfectly fine.
But docker pull nvcr.io/nvidia/tritonserver:19.09-py3 returned the same error as before.

Add up: The earliest version I can find on NGC is 20.03, I guess that’s why this error was generated. Then, how can I download version 19.10?