“Excellence is in the details. Give attention to the details and excellence will come”. Perry Paxton.
I would say this quote is the motto for all elite athletes and coaches.
As a video analysis coach, I am impressed with skaters who can keep high performance through years. I did a performance comparison of Vincent Zhou, 2017 World Junior Champion. The technique of his quad lutz did not change so much. We can see this easily with the 2 advanced stromotion below.
A little disclaimer about 2019, the original video quality caused me few troubles during the editing.
4Lz Vincent Zhou (USA), 2017 Cup of China, Short Program, advanced analysis.
4Lz Vincent Zhou (USA), 2019 World Championships, Free Skating, advanced analysis.
The speed before the jump is one of the key points for a quad. Unfortunately, this feature is difficult to collect from this kind of video/camera angle. Anyway, it seems that Vincent got more speed. In 2019, his upper body angle is a little bit lower ( around 55°, in 2017, he was around 47°). With the experience he gained, he became more confident with this quad jump.