Well when your work is in demand, and you are low production, sometimes a waiting list occurs. Sometime unexpected things occur during a build that hold things up. In my case, there were a couple things that caused some delays, but it wasn't anyone's fault. Just how things go. During my bass' build, a second body needed to be carved because Jerzy wasn't 100% satisfied with the first one. This required finding more wood, and then needed to be dried in a kiln before it could be worked.
Necks are left to acclimatize for months after initial carving to stabilize. Production basses usually get priority over custom basses. There are many factors. ...and Jerzy is a perfectionist and an artist as well as a craftsman, so he isn't just going to slap your sh1t together. In the end the buyer will get a bass that EXCEEDS their expectations. I can assure you. My bass was worth every penny, and worth every second that I waited for it.
also... if the OP did some research, he would have found out that 6 months is extraordinarily fast for Jerzy to complete a custom build. Just ask anyone in the JD club how long their custom basses took to complete. I suspect a misunderstanding in your build timeframe. It was likely "get started" within, or in 6 months time, and not completed. As you just placed your order a couple months ago, I am sure your bass will be at the bottom of the batting order, and that there are several basses in line ahead of you.
As I said .. relax. In the end your bass will be flawless, and awesome.