looks like latest version changed the path to letsencrypt binary has changed from letsencrypt/venv/bin/letsencrypt to relative .local/share/letsencrypt/bin/letsencrypt and options have been removed for --agree-eula and new option --agree-dev-preview added
changes for me in Centmin Mod Nginx server for letencrypt web root authentication https://community.centminmod.com/posts/19859/
so @chrisc might need to update your above guide 