How Many 2-Pin Base Configurations?

I have learned the hard way that there are at least two incompatible 2-pin CFL base configurations for use in 9 Watt fixtures. Are there even more?

I have a set of 9 Watt, 2-pin garage/driveway lights. I was frustrated to learn that all 9 Watt, 2-pin bulbs are not equal. I am tempted to replace the fixtures with some that accept screw-in CFLs. I'm certain that someone in engineering and/or marketing in the lamp and fixture business could offer a plausible sounding explanation for the proliferation of 2-pin sockets. I can understand there being different sockets for different wattage fixtures, so that an unwitting user could not overload the ballast in a fixture. More than one configuration for a given wattage is dumb. In the end it will doom the 2-pin configuration altogether. Think where we would be if every lamp maker and/or bulb maker insisted on a slightly different diameter or screw pitch for screw-in light bulbs!

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