The OG cover was issued only for peacekeeping troops wearing the OG (M65) uniform (IFOR), although theoretically it should be an issued item for every serviceman, especially because the "shiny" surface of the M70 helmet. But the average conscript soldier serving in Hungary has never seen such a helmet cover during his service. Anyway technically we can't name it as "experimental", because the issuing those covers was not an experiment, better a "limited use".
In comparison, we can call the OG M90 suit "experimental", because that uniform was issued to the troops as a large-scale troops' experiment. Just when the uniform was adopted, it was made in the recent 4 colour print pattern camo.