Ever wonder what the dates mean that you see within some of the Google search results? That date is generally called a fresh date, and it is the date that Google last crawled that page. So why do some results show a fresh date and some do not? According to Google sources, the date will only be listed for those pages that have been freshly crawled within 2-3 days of the date you are looking at the SERPs.
Not seeing a fresh date in your listing for a short time is nothing to be concerned about. It should be noted, however, that the disappearance of ALL fresh dates for all results seems to often be a harbinger of an upcoming update by Google, especially if the fresh dates disappear for more than a day.
