Re employment: The standard move for these companies was to basically auto-file a lawsuit if you were over a certain title threshold, and below they didn't do much. All the execs I knew would take a one year "vacation" and magically start work exactly 365 days later at the new company. It didn't affect rank and file except for this moonlighting + competition combo.
Re significance of 500 miles, state courts generally ruled that was a reasonable distance for non compete at the time, and so your company's lawyers would put together the most conservative contract that was borderline.
I'm very glad to have left that employment market, it was clear why startups never seemed to start in RTP unless they came out of Universities, specifically because of these huge liabilities for any investor. It's a shame, because the area now just waits for the next globo corp to open a remote office, rather than anything starting locally.
And what even is the significance of 500 miles when it comes to software?