I don’t know if this has ever been posted here before, but this is a fascinating article by Chris Aldrich.

The Mnemonic Major System and Gregg Shorthand Have the Same Underlying Structure!

The major (mneumonic) system generally works by converting numbers into consonant
sounds and then from there into words by adding vowels under the
overarching principle that images (of the words) can be remembered more
easily than the numbers themselves….

Gregg Shorthand is using EXACTLY the same consonant-type breakdown of the alphabet as the major system!