Eletrical fitting manufacturers.
I had to replace a two gang 1 way light switch earlier. In the original, there were six terminals - two COM, two L1 and two L2. In the replacement, there are also six terminals - two L1, two L2 and two L3. So, is it as simple as COM being renamed to L3? No. Old COM is now L1, Old L1 is now L2 and Old L2 is now L3. More confusing than you'd think.