Depends entirely on how much effort the company wants to put to enforce it legally. If a company has 2 customers, A and B, nothing's stopping them from sharing

Depends entirely on how much effort the company wants to put to enforce it legally. If a company has 2 customers, A and B, nothing's stopping them from sharing updates/patches with each other if 1 of them stops paying the license fee, and/or stripping the part of the code that phones home to check for a valid license. I think the key insight is, it's not worth focusing too much on this segment, except in very specific markets (maybe super-expensive sofware, like the Adobe suite, DAWs, AutoCAD etc.). The majority of paying clients don't go through this amount of effort, and unless they're cheapskates (in which case you might not want them as clients regardless), will just pay and be honest customers, appreciating regular updates and support.