Honestly, I think that a lot of the questions here about citation formats are mountains being made out of molehills, including (perhaps) this one. Remember why we provide citations:
- It is to help us remember where we found our ideas in the first place. I cannot tell you how many times I have had to look at my own bibliographies in order to remember where something came from, and how it worked. Having a good citation makes it possible to relearn something I knew once upon a time.
- It is to make it possible for future scholars to "check our work" and reproduce our results—in order to do this, they need to know how we came to the conclusions we came to, which includes knowing where our ideas came from. A citation tells that future scholar where to find the documents we used.
- It is to give credit to the researchers who came before us. Consider this part of the "gamification" of academia (since, for example, a tenure decision might be made on the basis of citation counts; also, it is just good etiquette to give credit where credit is due).
In all of the above cases, a citation which makes it possible to find the original source is all that is required. Generally speaking, author, title, and year is going to be enough. Maybe throw in a journal and/or publisher to make the Googling go faster. You don't need a DOI, and many older documents don't even have a DOI to reference. Sure, a DOI makes it faster and easier to find a document, but as long as there is sufficient information, it is fine to leave some fields blank.
That being said, if you are submitting a paper for publication, the journal will have standards for citations. Luckily, journals employ editors, whose job it is (in part) to ensure that these standards are met. If you submitting something, and you think that your citations might be insufficient, that is a conversation to be had between you and an editor. For all other cases, just make sure that you keep enough information to find the document again (e.g. author, title, year; DOI; a persistent link of some kind; etc), and don't sweat it.