these are system classes that are part of the product that do exists in the new installed version in the %SYS namespace.

If the Studio screenshot you have posted is not from the %SYS namespace (it really does not seems so), then probably the System package is mapped to that namespace, possibly also the related globals. But...I'm guessing here from the little details and context you provide.

For your response I assume you are searching for a class used by a Business Host component within a production.

Using IRIS you can search for that, and much more, using "Interface Reference" within the Management portal:

Unfortunately you are using an old version where this feature is not available.

Add this to the (possibly long) list of good reasons to move to IRIS.