I was under the impression that they still brewed or simply made the syrup on site. But a little research upholds your story (thanks for the clarification):
“The company behind the root beer has suffered a lot of changes. First the Galveston Brewing Company experienced a series of sales and name changes, eventually becoming the Triple XXX Corporation. Then in 1960, after the Food and Drug Administration ruled that sassafras (oil of saffron) was a suspected carcinogen, the Triple XXX Corporation scrambled to find a substitute with the flavor and foamy head characteristic of draft root beer, which the company was eventually able to do. Consolidation in the soft drink industry cut off many of the Triple XXX’s traditional direct-store delivery channels, and in 1985 production of bottled and canned Triple XXX Root Beer was suspended.
Today José gets his Triple XXX syrup from the Coca-Cola Company which is honoring a contract made when Triple XXX drive-ins graced many a small town. Sadly, most Triple XXX restaurants eventually gave way to the onslaught of fast-food outlets.”
source article