Even though it is a little fuzzy, you can see in this film about The Haunted Mansion (at 4:43) that when it opened in WDW it did not have a covered walkway. I don't know how long after the opening they added the cover for the queue, but, if the quality of the picture showing the skeleton of the cover is a clue, it was a little while after the opening. Perhaps when they figured out that standing in the sun was not good. HoP and CBJ were not really countable because they had an internal queue area, but, did have a covered western front for overflow. I couldn't find any picture of that, but, I am assuming it was built that way.
HMs queue cover was added before summer 1973. Same for HoP. And I believe for CBJ too.
The point being they learnt from that mistake 45 years ago.