I have "The Catholic's Guide," printed in 1946. It says fast and abstinence for the vigils of Pentecost, Assumption, All Saints, and Christmas, unless vigil falls on a Sunday. I've seen elsewhere that in the 1950s Dec 23 came to suffice instead of Dec 24. No mention of Immaculate Conception.
Also, I understand this source to say fast and abstinence on Ember Days (which are approaching), with no mention of ending at noon on Saturday.