Hey, here's an interesting read on the 594. I was wondering about your question and postulating the the 4 in 594 stood for the 4 control knobs. Nope, it's from the scale length of 24.594".
Anyway, I found this webpage interesting as it backed up suspicions I had held about vintage instruments. (Those instruments weren't vintage when those classic tones were produced).
Anyway, this thread has me seriously contemplating a 594 (one with curves!
). Great in sights.
https://heartbreakerguitars.com/blogs/heartbreaker-guitars-blog/the-prs-mccarty-594