Why didn't other people spot the the Game King double up bug in the Nestor case? If you think about that, it should help answer your question. They may have found the machines here in Vegas originally, but the denominations were too low, or they only had a few machines here in Vegas, or perhaps they were taken out quickly due to poor performance so they did some research and found out what other locations had the machines. The locations could have been posted up on the manufactures website even. Oftentimes they will say where they are installing their exciting new games.
Do you realize there are a few people who specialize in looking for ways to exploit bugs, glitches and vulnerabilities on slot machines? They know what to look for and probably keep updated on new machines hitting the market, especially machines from different manufacturers other than IGT.