Google’s John Mueller recommends following the company’s official structured data requirements to ensure content is eligible to be displayed as a rich result.
This topic was discussed in the latest instalment of the #AskGoogleWebmasters video series in which the following question was addressed:
In response, Mueller says it’s perfectly fine to use structured data properties that aren’t listed in the Google Developers site. Structured data that’s listed on the Developers site is what Google officially supports as rich results – there are numerous other types available for webmasters to use.
“[Do] we need to use structured data as per the Google Developers site (including required/recommended properties) or can we use more properties from Schema.org apart from the Developers site?”
With that said, if the goal is to have a web page be displayed as a rich result in Google, then following the company’s official requirements is highly recommended.
Though it’s important to keep in mind that utilizing structured data does not guarantee that a web page will be displayed as a rich result, it simply makes it eligible to be displayed as a rich result.
Using structured data types outside of what Google officially supports is optional, but also acceptable. Even if the structured data is not supported in the form of rich results, it still helps Google understand the content better and rank it accordingly.
Here’s how Mueller explains it:
“Independently, you’re always welcome to use structured data to provide better machine readable context for your pages. Which may not always result in visible changes, but can still help our systems to show your pages for relevant queries.”