First, there is a major difference between the component (e.g. the software package) and the connectors (e.g. APIs). It makes sense to talk about versioning at the component level, but it should rarely apply at the API level. See this excellent article for further clarification: https://www.mnot.net/blog/2011/10/25/web_api_versioning_smac....

Versioning an API is a decision by the API provider to let the consumer deal with forward and backward compatibility issues. I prefer the approach of focusing on the link relations or media type vice URI or some other technique of versioning because it is consistent in the direction (wrt Hypermedia-based APIs) of the link relations as the point-of-coupling for your API, which makes managing and reasoning about changes to your API less complicated.

Whenever possible, hypermedia-based media type designers should use the technique of extending to make modifications to a media type design. Extending a media type design means supporting compatibility. In other words, changes in the media type can be accomplished without causing crashes or misbehavior in existing client or server implementations. There are two forms of compatibility to consider when extending a media type: forward and backward.

Forward-compatible design changes are ones that are safe to add to the media type without adversely affecting previously existing implementations. Backward-compatible changes are ones that are safe to add to the media type design without adversely affecting future implementations.

In order to support both forward and backward compatibility, there are some general guidelines that should be followed when making changes to media type designs.
1) Existing design elements cannot be removed.
2) The meaning or processing of existing elements cannot be changed.
3) New design elements must be treated as optional.

In short favor extending the media type or link relation and focus on compatibility. Versioning a media type or link relation is essentially creating a new variation on the original, a new media type. Versioning a media type means making changes to the media type that will likely cause existing implementations of the original media type to “break” or misbehave in some significant way. Designers should only resort to versioning when there is no possible way to extend the media type design in order to achieve the required feature or functionality goals. Versioning should be seen as a last resort.

Any change to the design of a media type that does not meet the requirements previously described in are indications that a new version of the media type is needed. Examples of these changes are:
1) A change that alters the meaning or functionality of an existing feature or element.
2) A change that causes an existing element to disappear or become disallowed.
3) A change that converts an optional element into a required element.

While versioning a media type should be seen as a last resort, there are times when it is necessary. The following guidelines can help when creating a new version of a media type.
1) It should be easy to identify new versions of a media type.
a) application/vnd.custom+xml application/vnd.custom-v2+xml
b) application/custom+JSON;version=1 application/custom+JSON;version=2
c) * REQUEST *
PUT /users/1 HTTP/1.1
Host: www.example.org
Content-Type: application/vnd.custom+xml Length:xxx
Version: 2
…
2) Implementations should reject unsupported versions.

Hope this helps!