I read this piece by Frank Van Lenten long ago, and typed into my files. I then saved it on my blog in 2016. Mainly because he discussed his training in Isshinryu with Shimabuku Tatsuo.
I have never heard anyone from Isshinryu discuss it for accuracy.
I never met the man and have no other knowledge about him.
For some context here is an article about Frank VanLeten from Official Karate.