This really bugs me. I see companies advertising how many years of experience each of their principals has, and then those years are added up, and the ad says something like, "They have 530 years of experience between them!" *
What strange logic. Experience isn't cumulative in that way.
Heinz Wolfsburger has been working on Volkswagens for 30 years. He's taken courses on various VW models in Germany. He eats and dreams Volkswagens. He can resolve problems with Volkswagens that cause the experts at VW HQ to throw up their hands and drink too much beer. (Fortunately it's German beer, so that's okay.)
Meanwhile, on Facebook, a group of 1,000 Facebook friends, all of them 13 years old, and each of them with six months' experience tinkering with cars of various sorts, decide to form a virtual company named SomeDumbNameInvolvingDigitsAndTheLetterZ, or SDNIDATLZ. They create a snazzy Web site, advertising that they have a cumulative 500 years of experience fixing cars!!!!!
One day, your Volkswagen starts making strange noises and exhibiting other strange symptoms. Who ya gonna call? The pitiful wimp with a mere 30 years of experience, or SDNIDATLZ with 500 years!!!!
* Grammarians would say that, assuming there are more than two principals, the word should be "among", not "between", ** but never mind.
** American *** purists would insist that those commas should be inside the quotations marks, but never mind.
*** I was taught by South African purists.