I recently left a company where, when I was hired, I had agreed in "Appendix C" not to recruit any of their employees away from them for a period of 12 months after separation. When I actually separated after more than two years, the "Appendix C" they wanted me to sign and presented as the one I had agreed to at hire now said 24 months. I told them I was happy to stand by my original agreement of 12 months, but I had no incentive to extend to 24 and would not be doing so. They sent me one with the right number and I signed.
Their story was that, in the two years since I'd signed, they changed Appendix C and had "accidentally" given me the one that pertained to people who had been hired after me under the revised terms. I'm willing to give them the benefit of the doubt, because why believe people are malicious when they could just as well be careless?