Guys, recently I noticed a few differences between the SB18 movement in my enamel dial watch and the one in the Beihai. The positions of the gold chatons is different and the 3/4 plate is aligned differently.
So a quick text message to the Beijing manager and apparently the one in my watch is a newly-designed SB18, which is just starting to be produced and has not yet (or will never be - still unclear) been installed on the latest batches of the Beihai and Zhufeng.
According to them, the reliability and accuracy of this latest iteration is much better than the previous one. I also think it looks better as the 3/4 plate is now straighter and looks better with Chinese characters engraved on it, like a scroll. Beijing also said my CELADON Imperials made by them will have this new movement, which definitely made my day.