Dayan Qigong is a large system but also one of the most complete. I have a few years experience in this system now and believe that i can make a reasonable statement about it.
The different forms each have there own particular focus and follow a pattern of advancement in the system. There are movement orientated forms and still forms or meditations. Some of the forms are practiced together to increase the energy effect. e.g. Chest Releasing Fragrance Gong (movement gong) is best followed by Buddhism Releasing Fragrance Gong(meditative gong). These are advanced gongs and where formulated to refine and cultivate essence. In doing so Yin energy is released in the form of 5 different fragrances and the yang (essence) remains.
The 1st and 2nd 64 gongs are the primary sets and the basis for developing a solid foundation of health and for the curing and prevention of illness. They are the most popular and potentially all anyone need learn to provide you with a long and fruitful life. They cover both pre and postnatal energies and are a complete health care system in their own right.
When i first started training i didn't think i wanted to learn past the primary sets however the system is so natural and interesting that i have just continued on. It truly follows Taoist ideas and contains a lot of knowledge. It is a medical Qigong. It has its own martial system. It opens you up to higher level abilities such as healing others, prediction, visualising energy and ultimately enlightenment. It has a long and safe tradition which is proven and regarded very highly within China.
It is said that there are less than half the original syllabus remaining but i believe this to be untrue as there is a lot of knowledge, particularly in the healing and treatment side of the system that is not viewed as "forms" but is still an activity of the system and therefore could be regarded as other forms within the system. Hopefully all this knowledge can be documented and recorded for the future generations. Also it is believed that GM Yang Meijun transmitted different forms to differnet students. It is unclear as to why she would have done this.
Lastly I would like to say that in my opinion I do not think that the videos produced by Bingkun Hu are the best representation for practice and would suggest that you get a second opinion from other lineages of Grand Master Yang Miejun. The reason for this statement is that he states that he takes direct tuition from GM Yangs son, Chen. I have Bingkun Hu's video. Even in his video he says that he made the movements in the film more to how he was shown them, suggesting he has modified them, but it seem that he has gone way off the path. GM Yang wanted the movements unchanged and to her model. You can judge for yourself by comparing their youtube videos. They are however the only films available that show any forms other that the 1st and second 64 movements Kunlun Baqua and the meridian slapping.
I wouldn't normally make such a statement like this but I feel strongly that GM Yang wished that the system be kept as true to how she taught it and she only authorised a few people to teach her skill to others outside of China for that very reason. May I suggest that anyone who wants to know how to get these names to contact the Dayan Centre in Beijing and then get a teacher from that information or at least get a second opinion.
Lastly, thanks for your interest in Wild Goose Qigong. I hope this helps and if you want any more information then let me know.