Here is it:"Using structured data enables a feature to be present, it does not guarantee that it will be present. The Google algorithm tailors search results to create what it thinks is the best search experience for a user, depending on many variables, including search history, location, and device type. In some cases it may determine that one feature is more appropriate than another, or even that a plain blue link is best."
And example for Article:
there is field datePublished:
"The date and time the article was first published, in ISO 8601 format.
Best practices:
The date shouldn't change over time.
We recommend including the hour information in addition to the day in the timestamp.
The value for dateModified should be more recent than the value for datePublished."
and field dateModified.
But Google uses their own algos to show date in SERP.
Sometime it shows dataPublished, but based on different search query may display dataModified.
Peter