I have a couple of tubs of this, and noticed they were expired, so I wrote GSSI and this is what they had to say:
The recommended shelf life for Gatorade products like the Gatorade Endurance Formula indicates when the product is at its optimal freshness versus an expiration date. Gatorade beyond its recommended shelf life is safe to consume but may experience slight changes in flavor, color, or nutritional value.
If the product is sealed correctly and has no obvious off-color, flavor, or odor that would indicate product is not optimal, there is no reason why it cannot be consumed past recommended usage date.