It looks like there are many versions of public Microsoft SQL Server Linux version docker images.
I wrote a small script to check MSSQL version for all running containers and uploaded to github.
docker exec -t $container_id /opt/mssql-tools/bin/sqlcmd -U sa -P $passw
Below is sample output.
# ./mssql_docker_vers.sh Image: justin2004/mssql_server_tiny, Container: 1c4fc8c180af Microsoft SQL Server 2017 (RTM-CU15-GDR) (KB4505225) - 14.0.3192.2 (X64) Jun 15 2019 00:45:05 Copyright (C) 2017 Microsoft Corporation Developer Edition (64-bit) on Linux (Ubuntu 16.04.6 LTS)