If it's anything like other, non-food distribution, then they'll have their own in-house barcode system that cross-references whatever barcode system was used by the shipper and/or manufacturers (or packers or w/e). It's kind of silly IMO that there's no uniform inventory control system for everything one could possibly buy, sell, exchange, or transfer.
But companies have spent decades putting these systems together piecemeal, often using stupidly expensive proprietary software that doesn't know how to talk to any other software. So they're sure as hell not going to back out on the sunk cost fallacy now and invest in a whole new significantly more efficient system that will save them more money down the road. After all, corporate executives don't plan on sticking around in any one position long enough to bother with long-term planning.