When Neumann, Schoeps or Microtech Gefell talk about matched pairs, they really mean microphones with selected, matching pairs of capsules. They don't adjust microphones to match each other; they pick and choose pairs from among a production batch. Schoeps will select matching capsules (or CCMs) of any type on request, for a fee; for those models which Neumann sells as matched pairs, they typically choose amplifiers that have consecutive serial numbers as well--but that's mainly a vanity thing. When not specifically selected for a match, consecutive serial numbers don't even indicate that two items are from the same batch, let alone that their characteristics match.
With professional condenser microphones that have sonically neutral electronics (basically, any modular series with different interchangeable capsules), all the amplifiers of one given type should have essentially identical frequency response, while the gain should be within ca. 1 dB for the better brands whether they're from the same batch or not.
The greater variable is the capsule. Being electromechanical it has "a foot in both worlds" so to speak. Capsules vary both in frequency response (particularly at both ends of the range) and in sensitivity, and the extent of this variation generally exceeds the variation among amplifiers.
Sometimes two capsules match well in frequency response but not as well in sensitivity. In such cases it helps if you always put the more sensitive capsule onto the amplifier with the slightly lower gain, and vice versa.
The characteristics of capsules change somewhat over time, so a pair of capsules that was considered to be adequately matched (say) five years ago might not meet the manufacturer's matching criteria now. Unfortunately that's a fact of life.
--best regards