> Well, AFAIK, a four-digit identifier tells us [1:2] the year in which
> the blend was created, [3] the leaf quality [4] the factory number.

See, I was once told that too by a vendor. Since then, I've been told
it's used only for cataloguing to be able to identify a certain batch
of tea that was made by a factory. Some of the numbers are supposed to
correspond to certain factories, but I am not sure.