In a Starbucks TV commercial, I noticed the company notes it was founded in 1971. Here is a logo from their website that highlights 50 years of business:

The company’s website highlights their heritage:
Our story begins in 1971 along the cobblestone streets of Seattle’s historic Pike Place Market. It was here where Starbucks opened its first store, offering fresh-roasted coffee beans, tea and spices from around the world for our customers to take home. Our name was inspired by the classic tale, “Moby-Dick,” evoking the seafaring tradition of the early coffee traders.
Ten years later, a young New Yorker named Howard Schultz would walk through these doors and become captivated with Starbucks coffee from his first sip. After joining the company in 1982, a different cobblestone road would lead him to another discovery. It was on a trip to Milan in 1983 that Howard first experienced Italy’s coffeehouses, and he returned to Seattle inspired to bring the warmth and artistry of its coffee culture to Starbucks. By 1987, we swapped our brown aprons for green ones and embarked on our next chapter as a coffeehouse.
Starbucks would soon expand to Chicago and Vancouver, Canada and then on to California, Washington, D.C. and New York. By 1996, we would cross the Pacific to open our first store in Japan, followed by Europe in 1998 and China in 1999. Over the next two decades, we would grow to welcome millions of customers each week and become a part of the fabric of tens of thousands of neighborhoods all around the world. In everything we do, we are always dedicated to Our Mission: to inspire and nurture the human spirit – one person, one cup, and one neighborhood at a time
Fifty years is likely a safe point to highlight a founding date as it is a nice round number, a half century. Sure, 49 or 51 years gets at the same idea but it does not have the gravity of 50. Yet, I could imagine two sides to whether promoting this date is helpful.
On one side, fifty years is a long time. Many businesses do not make it this far. Even fewer companies are so long for so many years. Highlighting the date implies permanence, tradition, stability. Starbucks is not just a passing trend; they are good at what they do, they have been around five decades, and hope to be around for many more.
On the other side, Americans tend to like upstarts and novelty. Does fifty years imply old age and lack of innovation? Starbucks is established while other successful companies are offering new models and products. There are Starbucks locations everywhere but once companies like Sears or Woolworths also thrived.
Even as the company celebrates 50 years, companies are not permanent. Perhaps there is a time when fast food in general no longer exists or people can get similar food products at home. Or, Starbucks does something internally that causes issues. Or who knows what. Does it reach 75 years or 100 years, other round milestones worth celebrating? It is hard to know now; Starbucks will keep going until it doesn’t.