Interesting. First I've heard of it and I knew several people who knew Euphemia well and never mentioned it. In fact, one of them gave me an unpublished document by him on 14.1 strategy which I still have. Anyway, it must have been a very well kept secret among a select few.
Here's a thread from earlier this year on when some people knew about, or used, BHE: https://forums.azbilliards.com/showthread.php?t=491758