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(yes, this is official documentation)

It's still in draft. likely to change. Also, it's for the save api, won't get the required info there.

Is there a more canonical url for that doc’s info? Also, is the CDX api the proper endpoint for Wayback provenance data?

Don't know. However, You can keep track of the issue here: https://github.com/vegetableman/vandal/issues/8