The ocarina had achieved some popularity during the 19th and part of the 20th century in Europe and North America. However very little about what happened during this time period is common knowledge within the ocarina player community today.
There is also a problem that a lot of stories regarding the history of the ocarina which often get shared, lack citation of evidence, corroboration of multiple sources, or sharing of rationale behind a belief.
Thus, information that is stated as facts, may simply be 'old wives tales', or fabrications made up by ocarina sellers to create mystique and sell instruments. Things may actually be facts, but at this time we just don't know.
There is also the problem that a large portion of humans (common neurotypes), will copy whatever the majority belief is without ever stopping to question it. So misinformation can easily spread.
I feel that the history of the ocarina would benefit from some much more rigorous research. This should seek to find available sources of evidence, and make judgements based on that collectively.
Research should also be subject to peer review, as this will tend to reduce the effect of biases of individual researchers.
What published research currently exists? I am aware of the book 'Ocarina Mundial' by Simone Grassi and Francesco Coiro which is about the ocarina in Portugal and Brazil during the 19th century.