Shamanism is about Direct Experience
The level of authenticity for the shaman is directly related to the depth of his or her connection to the spirit world. It is also related to how present they are in the world around them. You can judge your shaman’s authenticity by whether or not they own the work or seem to be parroting methods from someone else.
For a long time, it was dangerous to be involved with healing that might label you a witch or something similar. As a result, many traditional practices went under ground, or were completely lost, because it wasn’t safe to practice them.
Nor would it be particularly a good idea to go over the the nearest native healer, grab up and run off with their healing practices. (This is referred to as Cultural Appropriation.) For one, its not always possible to properly understand the traditions of a culture you did not grow up in. Secondly, the traditions of another culture may not be appropriate or authentic for that person. Finally, the practice of another culture has a wholeness and integrity, and it can be dis-empowering and disrespectful to break it into usable pieces that make sense to you.
Luckily, this is where the very nature of shamanism comes to the rescue. Shamanism is a direct experience of the spirit world and of spiritual truths. The shaman learns by communicating with and receiving guidance directly from the spirit world. The shaman goes directly to their spirit teachers to learn methods and approaches that are unique to that shaman and to those spirits.
Even in days past, it was not unusual for a shaman to find themselves without a living human teacher to guide them. Maybe they lived in a remote location. Maybe, the last shaman died before he or she could pass on any knowledge. So its not a new thing that shamans learn without the benefit of traditions. In most cases, even when you are studying within a tradition, the spirits probably have a few ideas of their own and will guide a shaman to try unique things.
Some traditions have very specific rules, because repeating a specific ceremony in a specific way builds power through repetition. Often, for an outsider to become part of a traditional healing system, they have to join and belong to that healing system to be authentic. But there is a different and equal power in working in new ways. It is possible for a shaman to learn everything they need to know directly from the spirits, without any human guided training. That’s not to say a shaman shouldn’t go and get some training. Training can help a healer learn some of the things that might other wise have to be found by the trail and error method…