More and more it seems, online publishers (yes, you are a publisher) are publishing content without showing a (prominent) last-modified date. Why is that? And, more importantly, should you follow suit?
Why hide the date?
Without asking each and every one for the rationale behind this choice, I can make an educated guess:
For most readers, the date strongly indicates the content's relevance. If you are doing online research, would you take the time to read a SEO piece from 2013? Would you read any Social Media piece from 2014? Probably not.
The last few years, large groups have joined the Content Marketing movement—and rightly so. The Content Shock (full disclosure: published in 2014) has forced anyone doing serious online research to excel in content curation: weeding out the irrelevant from the excellent in seconds.
On search, Google will try to show the publication date of your content in the result list. Google will show the Title, URL, Date and a (Rich) Snippet, and the reader will use all that to rank the results:
Figure 1. If you are researching CMSes, which would you open?
It doesn’t seem like Google puts a big penalty on not having an (explicit) date, or on aging content, which is a bit strange to me: I have tweaked SOLR searches and usually the date weighs heavy in the relevance score.
But your content is evergreen, and time will not wither away its brilliance? Hiding the date from your publication could help you retain traffic to your hard-earned jewels.
Your implicit promise
Removing dates from your content prohibits me from using its age to ascertain its relevance. You, as a publisher, are making me, the reader, an implicit promise that I will not be disappointed in the timely relevance of your content.
This is a promise that is hard to uphold. Do you check your old content for relevance? Do you update your content to remain relevant? Do you unpublish aged content?
Having implemented many CMSes at a diversity of large content organizations, I know that this is rarely the case. The processes are not in place to do so, and the tools to support such processes are usually poor.
So: To date or not to date?
So, it could be that you are that one writer that keeps all your content crisp. Brilliant! I want to read! In that case, use your last-modified date to show me your hard work.
Do you fire and forget? No problem! Also put include your last-modified date—which will be equal to your published-on date.
Does your content have an extended shelf life? Kudos to you! I hope you have (or build) a reputation for this. I personally have no problem in sharing wayback content from big names—although they will have probably produced something better already.
If you want to provide relevant content to your readers, show the last-modified date. And set it at the beginning of your content so Google and your reader can use it. Google will help you here, because it puts greater value on the last-modified date than the published-on date.
Here's a nice read on experimenting the use of dates: Should You Remove the Dates From Your Blog Posts? (2013) Somebody was sorry sharing a 5-year-old piece, without considering it could still be relevant.
Do read the discussion section, including where they say that Twitter users hesitate to tweet anything over 14 days and make other good points about why to not date your content. Usually, it boils down to the “image” of the publisher. Relevance is in the eye of the reader.