Forgive my ignorance of the nuances of the 3 tier system, but does the distributor not purchase the beer from the brewery, then sell it to a retailer? So if the beer sits and goes out of date, one would assume that either the retailer or distributor would eat the cost (assuming they actually pull the product, which has not been my experience) instead of the brewer?
I'm not saying I know one way or the other, just making assumptions
Not sure about alcohol, but many distribution contracts for perishable products include clauses that say that if the product doesn't sell and goes out of date then the distributor doesn't have to pay for it. If not perishable, the distributor can often return the product later. That, and the brewery will often end up paying because they care the most about maintaining freshness.