Pyrioni, that's been my experience with any well-made headjoint...if you change headjoints, you will learn new ways to use your embouchure. When you come back to the 'old' headjoint, you may like it a lot better than you did before. It's funny, sometimes you need to upgrade from the student CY (for example to the Sankyo NRS-1) because you reach a plateau in your learning, the student headjoint may be holding you back. But that's the cool thing about the CY, or any other well made headjoint-after you become very proficient on another headjoint, you can come back to the flute that was holding you back and get lovely things out of it.
I believe they designed the CY cut to be fairly basic but very flexible in terms of playability. It was the 'pro' cut a while back, and Yamaha's best flutes came with a handcut CY headjoint. I know there are some really nice handcut ones out there. The student flutes have a machine-cut CY headjoint, but they are very consistent and very playable. Lots of pros have a Yamaha student flute as a backup/play outdoors instrument, and it is probably because so many different flutists can be satisfied to play well on it, though they may prefer their 'fancy' flute.
Thank you Tibbiecow for explaining in great details. You are right, may be I got stuck in that bottle neck 5 years on my 211's CY cut, then 18 months on Sankyo's NRS-1 finally freed my embouchure.
Yes, I heard many good things about CY cut from my teachers, friends and on the internet too. You are so right, many people in my country said that they used CY cut to get good grades and even entered best conservatories in the past, I think the former model of 211 was F-100?
And high-end Yamaha model still provide CY, EC or BC as options. So, CY cut must be a good option for professional players. We students are so lucky to have CY cut with suck low price, machine made are very consistent because I heard they were cut with high precision computerised lathe.
Many people said the student CY cut is rather slow in response because the drop-off-plate are in normal round-shape and the blowing angle is not steep enough, but in fact this is a good advantage, because the intonation fluctuation will be less on CY cut ~easier to control; Also according to Canadian Master Robert Aitken (during his masterclass last year) he said the slow responsive headjoint is actually a good headjoint, because you can control it more easily and give it more subtle details and more colour changes.