Different types of Hi-Gain pickups?

[bails]

Which year did Rick' change their Hi-Gains from the smooth black plastic tops(surrounding the poles) to the ones with a raised ridge on each side of the poles? I assume the raised ridge is there because it's the same molded plastic housing used in the reissue toasters. Is there any difference between ridged Hi-gains and the older smooth-top Hi-gains?
note: Peter McCormack's "Silver Dream" 1988 4003 Silver shows smooth-top Hi-Gains and conversely "Endless Love" 1993 350 Liverpool MapleGlo clearly shows ridged Hi-Gains.