It's all about experience. When I first took the BJCP exam any style above 6% was illegal to sell in NC. As you can imagine tasting those beers was a challenge. In the end what dragged down my initial taste exam score was not my ability to sense, it was my ability to fill out the score sheet. I never made that mistake again and over time I improved. At one time I felt ill prepared to judge certain categories - meads, ciders, etc., but over time I've gotten to the point I'm good with judging anything. Can I do an excellent job of telling a cidermaker how to improve in process? No, but I can tell them what they should eliminate or add, or where I believe things went wrong. I can pretty much judge anything given a set of style guidelines and I'm sure many other judges are in the same boat.
What will be challenging once the guidelines are established across all competitions will be the BOS round. When that Piwo Grodziskie hits the table I'm going to have to reference the guidelines. With the completely new numbering system I suspect BOS rounds will slow down until people become familiar with them. I never took the time to memorize the 2008 numbers so I probably won't wast time on the 2015. I will take the time to read and comprehend all the styles, but remembering what is 9B isn't going to help me judge beer in a glass, it will however help speed up a BOS round, but some beer geek at the table will have those set in memory after a few comps.