The Assyrian Church of the East, aka the Nestorian Church, is different from all other churches in quite a few ways. They broke off in 431, which was pretty late for the development of Christianity but pretty early in time.
First off, they do not have the bishop or a patriarch make and bless holy chrism on Holy Thursday. They just “refresh” the chrism from the previous year by adding more oil and ingredients. In this way, they believe that they possess chrism from the time of the Apostles.
(However, nobody seems to have been doing this before the Nestorians broke off, so I have to conclude that it was more a way of keeping the chrism going when they couldn’t get new chrism from a patriarch or bishop.)
Second, they also preserve a stock of sourdough leaven or yeast mother, using this same stock for the making of their leavened Communion loaves/Hosts, and only “refreshing” it from time to time by feeding it or sharing stock from another parish. That’s the “Holy Leaven,” which they also believe comes down from the Apostles.
(But again, nobody in the ancient Christian world was doing this, so it’s unlikely to come from the actual Apostles. However, it is perfectly normal in the Eastern Catholic world to use leavened loaves for Communion, so there’s nothing weird about that.)
Likewise, they say the Sign of the Cross is a Sacrament, but nobody else does. It’s another isolation thing that came from their separation. Nothing wrong with it, just different.
So it doesn’t really say anything about the development of Sacraments, other than that “If a group goes off by itself for several hundred years, it will develop new customs and traditions.”
