You're posting was very interestign, and gives me worthwhile leads. However, I must note:
You're exerpt is from someone who uses the word, "Romish." The use of a non-standard perjorative doesn't speak well of someone's frame of references when they make unfounded assertions ("we have reason to believe...") Of the groups they identify, there is much better reason to quabble than what would be merely ad-hominem:
I think you'll certainly agree that the Cathari aren't Christian, given the denial of the divinity of Christ.
Of the Passiginian, they are plainly Judaizers, whether or not they circumcised, and from my limited understanding, were a short-lived an local phenomenon.
A.H. Newman regularly admits that the Ethiopes did keep Sunday. Their use of Saturday as a day of rest is not far from our concept of "weekend;" Copts certainly keep the day of Resurrection, Sunday, as most Holy.
As to Chaldean Catholics (A non-Latin rite of the Roman Church) and the Armenian (An Eastern Orthodox branch), I can attest from personal witness that they keep Sunday holy.
I am ignorant as to the ancient Chinese Christians, but remain dubious given the above facts.
There are several sites on the internet that I looked at. I happened to choose this one because it succinctly summarized some groups that were thought to keep the sabbath during the time period in question. I had no idea the term "Romish" was considered an insult. I'm not sure if the author meant it as an insult or as a term referring to the church in Rome.
As for the rest of the post, I'm not going to analyze the believes and practices of each group. I'm certain that the church/state in prominence at the time wouldn't necessarily portray their beliefs in a fair and unbiased manner.