Appian Documentation for older releases

@akshayan you can directly visit this  URL and click on Appian Version dropdown and choose your desired Appian Version to view it's Documentation.

 

Attaching the screenshot of dropdown at the mention URL to switch the Documentation for various documentation.

Thanks for the reply, appreciate it! If I select 16.2, it takes me to forum.appian.com and it throws "Error 401 - Unauthorized. Sorry, your request could not be processed". I have sent an email to community@appian.com and waiting for a response.

Thanks for the reply, appreciate it! If I select 16.2, it takes me to forum.appian.com and it throws "Error 401 - Unauthorized. Sorry, your request could not be processed". I have sent an email to community@appian.com and waiting for a response.

akshayan earlier i was also facing similar issue, not exactly same but yes, So i too sent a mail to community, and they have resolved the issue.
So it's not the issue from your side, since the community recently launched hence, it may take some time to get stable and to get integrate.

as per your statement i think, currently you are not able to access forum.appian.com also. You can expect a better response from Appian Community on this concern.