Yes, the 200 replaced the 100. The 100 used 6ER5 tubes and the 200 used the classic 12AX7. I'm only guessing here, but I'll bet George got tired of people complaining about the noisy 6ER5 tubes. In the very beginning, he could have just designed a 12AX7 preamp like everyone else. But, he didn't because the 6ER5 was a superior way to go for a more transparent and alive sound. This tube was never designed for audio use, so it can be difficult to find a quiet set. But, when you do... this is what makes the sound of the 100C so special. I'd never trade my 100 for a 200.
Now, I hate to repeat myself because I bring this up every time a post shows up about these preamps. I am on a personal cusade to tell the world that you must try using this pre directly into the amplifier's input instead of through a linestage. The 12AU7 output tubes have plenty of oomph to drive an amp directly. You have removed tons of redundant circuitry and cabling from the system. It's a whole 'nother animal. Use the gain pots for volume control.