In the previous century Laws concerning Fasting and Abstinence have changed considerably and at different intervals.
Pope St John XXIII altered the rules for fasting and abstinence in 1966 with his Apostolic Constitution PAENITEMINI.
II. 1. The time of Lent preserves its penitential character. The days of penitence to be observed under obligation throughout the Church are all Fridays and Ash Wednesday, that is to say the first days of "Grande Quaresima" (Great Lent), according to the diversity of the rites. Their substantial observance binds gravely.
- Apart from the faculties referred to in VI and VIII regarding the manner of fulfilling the precept of penitence on such days, abstinence is to be observed on every Friday which does not fall on a day of obligation, while abstinence and fast is to be observed on Ash Wednesday or, according to the various practices of the rites, on the first day of "Grande Quaresima" (Great Lent) and on Good Friday.
More Closer to home for you in Wisconsin can be seen here:
In the USA:
In Paenitemini, Pope Paul VI gave authority to the episcopal conferences on how the universal rules would be applied in their region. On November 18, 1966, the National Conference of Catholic Bishops legislated the following to be observed in the United States:
•Abstinence is obligatory on all Fridays of Lent, except Solemnities (i.e., I Class Feasts).
•Fasting and abstinence are obligatory on Ash Wednesday and Good Friday.
•Abstinence on all Fridays, though not obligatory under pain of sin, is “especially recommended.”
•Fasting on all weekdays of Lent, though not obligatory under pain of sin, is “strongly recommended.”
The local ordinaries also have authority to grant dispensations from these rules within their dioceses.
All this being seen and more through the Church's legislation on fasting and abstinence, there is nothing stated officially as to what the faithful must or must not give up during Lent as a form of penance. As I mentioned in my comment I know many Catholics in various countries that practice giving something up for the entire Lenten season, while some follow the Sunday exception rule, seeing that Sundays have never been a day of fasting in the Church.
Where the idea that Catholics can have a break from their personal Lenten disciplines on Sunday originate, I fear can not be traced to a specific place or time since it was most subtle in coming about.