Even though all the mic's are built the same, the parts that make up the mic are manufactured with certian tolerances. some resistors may "resist" a little more or less than others. As long as they are within a certian range, they are acceptable. This is true with all the parts that make up a mic. A matched pair of mics is just a pair that sound the same and give a similar signal when tested. You may be able to get a factory matched pair, but if not, you can go into a music store and test your own. Hook up one mic to a pre, I'd suggest a mixer or something where you can see the input level. test the mic and listen through headphones. Notice the LEDs on the mixer. How strong is your signal when you test the mic. How clear is it in the headphones. Now...take a second mic and test it the same way. Do you get the same signal on the LEDs? Does it sound as good in your headphones?