The popping sound familiar from many jars only occurs with products that are filled in a vacuum closing system. Here, the product is heated before it is filled into the jar. When the product then cools down again, the air in the jar contracts and a vacuum is created. This causes the lid to be tightened. When it is opened for the first time, air enters the jar again and the vacuum escapes. This produces the familiar plopping sound.
If jars are to be sealed without a vacuum, only the lid is heated instead of the product. This causes the layer of material integrated in the lid to soften and adhere to the jar when it is sealed. Since no vacuum is created in the jar during this process, the jars are somewhat easier to unscrew and accordingly no popping sound is heard when opening. The vacuum-free sealing technique allows the product to be filled in a way that is gentle on the nutrients, as it does not undergo any additional heating.
So if our jars of nut puree don't pop when you open them, that's by no means a quality or freshness defect. Nut pure es keep perfectly well without a vacuum due to their high fat content. The naturally settling oil layer also acts as protection against oxygen ingress and thus preserves.
By the way, you can easily tell if a product has been filled in a vacuum sealer by looking at the lid: Vacuum-sealed jars have additional bulges on the lid. Jars that are sealed without vacuum, on the other hand, can be recognized by a lid with a smooth surface and the KoRo quality seal.