What is the meaning of the numbers on the back of green tea boxes?
Doesn't matter which brand. These numbers indicate exactly which tea and which grade of the tea has been used. It is part of the ISO9001 certified tea trading companies in China.

Similar to ingredient lists, the most used item comes first. This blend of green tea uses several grades and series of leaves of chunmee, from the highest grade to intermediate grades.

The same goes for the gunpowder tea.

The reason it's so hard to find info on the Internet is because it's chinese. But you can rest assured it means you are get good quality and reliable tea.