Whenever a manufacturer has a series of condenser microphones that is modular--i.e. with various capsules that are interchangeable on the same amplifiers (bodies)--then those amplifiers are normally designed to have very flat frequency response, perhaps with some filtering at the high and/or low frequency end of the response range. Any two properly functioning microphone amplifiers from a series like that shouldn't vary in their frequency response by more than a tiny fraction of a dB, most likely at one or the other of the frequency extremes.
But the gain of two such amplifiers may differ by some greater fraction of a dB, even with the highest-quality brands. For the best brands of studio microphones, the amplifier gain might be consistent to within ±0.5 dB, for example--but that would still allow two such amplifiers to differ by about 1 dB in the statistical worst case.
Still, condenser microphone capsules typically vary in their sensitivity by even greater amounts (thus the main argument for having one's capsules selected as matched pairs). In any given pair of modular microphones of the same type, there will usually be one pairing of capsules with amplifiers that results in a closer match, while the other possible pairing results in a less close match. Since I very often do stereo recording with only two microphones, I find it worthwhile to figure out which pairing gives me the better match between channels.
--best regards