Further to part 1, you can skip the authors but must read and learn 天玉经，青囊经，都天寶照经 etc.
Here, with reference to 天玉经： 江东一卦从来吉，八神四个一， 沈：解为江者坎，(壬，阳顺）江东一卦为地元龙 （ note: 地元 is only 武曲六运卦）Then 破军左辅？。His description: 壬丙甲庚丑未辰戌 (his 八神) which some doesn't tally. The fact that 江东卦 are 1(父母）, 6,7,8。 1 卦 being 八神 （乾，兑，离，震，巽，坎，艮，坤）。四个一 是变一爻
Note: The writer's era/period. (Shen 1920s)
Again: (Note the original script period 唐朝末) 江西一卦排龙位，八神四个二。沈解：天人两卦， 八神者 （子癸，午丁，卯乙，酉辛，艮寅，坤申，巽巳，乾亥）. Was there any consideration into 升观睽革?
Firstly, the difference of 八神 （In the context of 八神, 沈has his meaning). Secondly, note that 沈 mentioned 江东地元 (八神：壬丙甲庚丑未辰戌）， 江西天人元 and then 南北父母 (back to the above乾至坤)?
Let's explore some authors‘ specific understanding and their explanation （in order to save time, just on 八神四个二）:
1) 蒋：。。。经四位而起父母，故曰八神四个二者，此一卦兼管二卦之事，而不能全收三卦也，比如坎至巽乃第四位，巽至兑即第第四位。。
2）谈：。。。四个二为八，八为艮，即山泽为江西一卦也。。
3）陈：。。。江西一卦，八神中也有四个入用，但两两各一小组，分别入于同的两卦之中。。
Now do you see how their concept originate? Do they interpret as per original script writer's intention/ knowledge?
There's a need to understand the basic: 阳从左边团团转，阴从右路转相通
I have given you quite obvious answer where to search for. To explain further, there is no point for you to learn anymore. There are many masters who have made commentaries on this. The most imporant thing is that whatever you learn, it works.
I leave you to scratch your head. If you want to adamantly follow 沈 without investigating into the differences, then its up to you. 记：一通百通 , 可别 “不通钻洞”。