Here are some info I got from a tea seller:-
1) Spring Puerh does not carry bitterness. If it is bitter, it is not spring Puerh
2) The date printed on the packing of the Puerh does not necessary mean it is from Spring. The date is referred to packing date. This makes it even harder to identify

3) Packing of some small factories are totally ridiculous and non standardized. I have experience seeing Puerh of the exact same packing and dates but was told that the inner Puerh is of different season. Price range is so much different.
4) It has to come down to tasting the Puerh. Problem is, how are you sure by tasting it even with no bitterness it is Spring?
So what is your opinion? How do you select?