I think that a lot of articles can be written without a date if they are content that is close to being totally evergreen. If you add a date to these articles and that date is a few years old, it can tarnish the opinion of the visitor when there is nothing wrong with the article, and the article might even be among the very best on the web. So, I don't date a lot of my articles for that reason.
I am always upgrading articles, which is different from updating. An update is when you add fresh news or information that is totally new about the subject. An upgrade is when you add another section of evergreen content, add new photos, improve photos, add a video, do a rewrite for clarity, or other type of improvement. I notice that when I upgrade an article it often moves higher in the SERPs. Usually just a few positions if it is on the first page, but if it is deep in the SERPs, it might move up substantially. I've never had anything move from bottom of first page to #1, unless it moved into the featured snippet.
If you have a website with a few thousand articles and your author team is two or three people, if each of them update or upgrade one article every working day, there will be articles on your site that go a long time without an update. Figure 200 working days in a year and a three person team.... if you have a 6000 article website that means it will take ten years to upgrade or update every article - if you do them in a straight rotation.