This issue was not limited to icing reefers, the original air conditioning systems on passenger cars required ice as well. While so far as I know none of the ng. equipment was ever air conditioned, I do have pictures of a baggage cart parked next to a heavyweight CN sleeper and the blocks of ice are indeed being manhandled up to the top of the car and into the ice bunker. And that was in 1966. I mention that only because it indicates it could and was done without a dock.
I saw reefers in service on the DRGW ng. into the 1960's so presumably some kind of icing arrangement was maintained until then. Have no idea how long the icing facilities John cited lasted. I'm guessing the Alamosa facility may have lasted into the 60's because there was a lot of outbound standard gauge perishable business out of the valley in those days, and I don't think (standard gauge) mechanical reefers became common until the late 60's.