The publications/items found in the National Guidelines Clearinghouse are summaries, Most of the guideline summaries in the National Guideline Clearinghouse are actually journal articles and it is best to find the original source when possible.
Links to Directly to APA Citation Style, 7th edition - Research Guides at George Washington University
DOI (Digital Object Identifier) has only been around since around 2000 and not all articles/publications have a DOI.
It is a unique alphanumeric string assigned by a registration agency (the International DOI Foundation) to identify content and provide a persistent link to its location on the internet.
The rules for DOIs have been updated in the 7th edition of the Publication Manual of the American Psychological Association. They should be included as URLs, rather than just the alphanumeric string.