Employee anniversaries were celebrated and featured in TekTalk and TekWeek. This May 1957 TekTalk features Howard Gault as the first 10 year anniversary. Its a bit confusing because he is the first employee, e.g. non-founder, to reach 10 years. Howard, Jack, and Miles all reached 10 years prior. This explanation comes from the Winning With People: The First 40 Years book by Marshall Lee.
This November 1957 TekTalk features two 10 year anniversaries.
This December 1957 TekTalk features one 10 year anniversary.