Adobe have restored CC 2017 as a Previous Version to your Creative Cloud desktop app.
Last week, when they released CC 2018, they removed the ability to install CC 2017 or earlier from the Creative Cloud app. Being able to do this makes it easy to manage systems where people are using different versions, finishing old projects before upgrading, etc.
The earlier versions are not available – so the few of you with CC 2013, 2014 and 2015 who need to keep those for any reason, should be careful. We’ve saved package installers for our clients, just in case. If you’re still using older versions, you should think about doing the same.
When installing 2018, it will uninstall the previous versions by default. As Steve Pelluet said in his comment on my last post about this, if you want to keep your previous version alongside 2018, click the twirly after hitting the install button and uncheck “Remove previous version”.