dbx had two general "families" of processors: pro and consumer. The two were based on similar principles, but the implementations were incompatible with one another (different bandpass filtering, frequency weighting and response time for the level sensing circuits). The consumer units were designed to be a little more tolerant of typical frequency response errors in playback, and a little less likely to cause severe tape saturation when used with slow-speed tape recorders (3-3/4 ips open reel, or cassette).
In theory, any consumer dbx decoder should have been able to decode any recording made with any consumer dbx encoder, and likewise for the pro units. But they kept changing the circuit parameters between models, such that any given recording might really not sound right unless it was played back through the same model processor that had been used to make the recording in the first place. It got so bad that some engineers would send their dbx processors along with their master tapes when LPs were going to be cut from them.