I didn’t know about "Petö Proverbs" myself until recently. I discovered their existance when I was re-reading one of the early copies of The Conductor magazine that was published by the Foundation for Conductive Education in its early years.
“Petö’s Proverbs” is said a bit tongue in cheek because no one knows what Petö actually said, apart from the people he actually said it to. It is now over forty years since his death. How can we know what people’s memories do?
The Petö Proverbs that I have are something that Ester Cotton compiled in 1969, two years after Petö’s death. There is quite a mystery about this collection as I believe there is another version in the Foundation Library attributed to James House, that I have never seen.
It could be that Petö wrote to Ester Cotton, it could be that he spoke to her during her visits to the Petö Institute, but as there are no records the source could be neither of these.