The AFL-CIO closed the book on 2012 last month with its annual membership report, documenting the fortunes of its 57 affiliate unions. It’s probably not a story the federation is happy to tell, given that it lost about 70,000 net members for the year.

Still, the report did make sure to highlight some recent gains: Although 25 affiliates lost members in 2012, 16 showed membership increases, and 16 showed no change. The report also hailed individual successes, such as UNITE HERE and National Nurses United, each of which gained more than 10,000 members in 2012.

That got me to thinking: We’ve been saving these reports for a long time, and therefore have the AFL-CIO’s membership data going back all the way to 1955 (at least in five- or 10-year intervals, depending on how old the reports are). Are there any affiliates around today that are truly at the head of the membership class? That have never had so much as a five-year dip in their numbers in almost 60 years?

The answer is yes. There are three AFL-CIO unions that have increased in membership at every five- or 10-year interval since 1955. (I didn’t pay attention to any year-to-year fluctuations.) The American Federation of Teachers, which started out as the 25th-largest affiliate in 1955, has grown almost thirtyfold through the years, and now ranks second in the federation. The International Association of Fire Fighters and the International Alliance of Theatrical Stage Employees (which covers theatrical stage employees and film technicians) also have grown continually since 1955, albeit on a smaller scale than AFT.

On the flip side, no affiliates have lost members continually since 1955. But that’s only because they haven’t been around that long. Well, the United Auto Workers have, but they disaffiliated in 1968 and didn’t return until 1981. But at every five- or 10-year mark that it appeared in the AFL-CIO’s books, the UAW reported fewer and fewer members. Similarly unblemished records—so to speak—belong to Glass, Molders, Pottery, Plastics and Allied Workers, which started in 1965; and Bakery, Confectionary and Tobacco Workers and Grain Millers, which debuted in 1985.

Honorable—and curious—mention goes to the Plumbers and Pipefitters union, which managed to stop a two-decade slide in 1995 and has posted the exact same membership total—219,800—every year since.