Though she said it in reference to her own invention, Speedwriting, in one of her books from 1927, Emma Dearborn said something that fully applies to Gregg:
"A chain is only as strong as its weakest link; and YOUR shorthand is only as good as the most troublesome word in it."
Can you imagine?! Here I am living in fear of the thousands of words out there just waiting to turn up and stop me cold, words that I won't live long enough to have practiced specifically and individually.
SO, the only hope I see is a nice, handy list of TYPES of words or even just sound combinations that number in maybe the hundreds, hopefully even less than that, so we are prepared to easily write previously unpracticed words.
P.S. I don't mean stuff like "analogical word endings", etc. because the problem is just as likely to come up in the front end of the word as at its end, just some pesky connection like turning "s" the wrong way before the following consonant.