It is normal for invoiced weights to be a little bit different from what you actually get out of the bag and it's also common for invoiced weights to be a little different from the bag markings. Before becoming too concerned it's best to double check against documents. As you buy more sacks some will be a little over, some will be a little under. It will almost never be exact to the gram. Contracts are generally written such that you're expecting delivered weights within a half percent, but that's not the same situation as picking up a single sack on the spot market. You're not getting the benefit of variations averaging out over the lot.
The difference that you're describing for a single bag is high, but it's not surprising. It's possible that at some point there was damage to the bag and some coffee fell out. It's possible that coffee was pulled from that bag for samples. Some members of the supply chain are more accurate than others when it comes to filling the bags or tracking loss in transit. A little bit of that might also be that coffee is not some static, unchanging thing. The weight will change over time depending on storage conditions.
