I can’t find the DOI for anything from the IAF’s International Astronautical Congress

When looking for papers from the IAF’s International Astronautical Congress, there is no DOI landing page, but rather a note saying, ” If you would like to purchase an IAC paper please e-mail us the information regarding the paper of interest to the e-mail address: [iac_archive@iafastro.org](mailto:iac_archive@iafastro.org).” Does this mean they are not registered with a DOI?

Is there any other way to get access to the papers from this conference?

[http://www.iafastro.org/publications/iac-papers/](http://www.iafastro.org/publications/iac-papers/)