CONSO
You are perfectly correct, so long as the CVR continues to record for a few seconds after the initial pressure wave from either an explosion or explosive decompression. If the explosion or decompression event severs the data lines to the CVR at the instant it happens, only an initial high spike will be recorded and the remainder of the data is lost. So the vital reverberation information that would distinguish between an explosion or explosive decompression is not available for analysis.
It may be possible to estimate the strength of the initial leading edge of the pressure wave from the rise time before the signal to the CVR was lost. Slight time delays between the different microphone pickups can be used to localise the source. The further away the noise originated, the less accurate this will be. So an event at the rear of the aircraft can be positively identified as originating from that area, but whether it was behind the wing, in a rear baggage hold, or in the tail section will be very difficult to establish with any degree of accuracy.