Here's the reply I received from a B-I-B vendor:
Regarding your question about the longevity of wine stored in our 5L bag-in-box packaging, typically, these bags are designed to keep the wine fresh for about 6 to 8 weeks after opening. This is due to the vacuum-sealed nature of the bag, which significantly reduces the wine's exposure to air, a primary factor in the oxidation process that can lead to spoilage.
It's worth noting that the shelf life can vary depending on a few factors, including the type of wine, the storage conditions, and how often the bag is accessed. To maximize the freshness of your wine, we recommend storing the bag-in-box in a cool, dark place and ensuring the tap is appropriately sealed after each use.
If the wine is unopened, stored in optimal conditions (cool and dark), the bag-in-box can keep it in good condition for up to 2 years, though we always recommend enjoying it closer to the time of purchase for the best taste.