Quality of the mine depends on the seller

We already use the mines for years, and depending on the source of income the mines of very good or very poor quality can be.
The last mines were acquired by a private seller who has leave probably long. In this case, these were 100% Ausschussware: All mines were dried and wrote only a short time.

Storage temperature and age are the decisive factors.
When the mines not protected from drying or stored too cold or too warm. Are you going to use any more.

The quality of mine is - it inferentially - not the manufacturer, but the seller must make the realistic details of the product (age, origin, storage).