I was an IPSC target supplier for a few years and my understanding was that the reason for perforations was to reduce visibility. Te perfs were to only to through the first layer to avoid weakening the target.
The IPSC targets varied depending upon where they were produced and the type of die used. Rotary dies are fast but inaccurate. Moisture can affect the cardboard and change the distance between perf zones as well as the depth.