Prior to the reform of the liturgical calendar in 1969, the Feast of the Most Precious Blood of Our Lord Jesus Christ was celebrated on July 1. (It still is by those who follow the 1962 Roman Missal in the Extraordinary Form of the Latin Rite). At the time of the post-conciliar reform, it was determined that this relatively modern feast, only part of the Church’s universal calendar since 1849, be celebrated in union with the annual observance of Corpus Christi. In order to make the change clear, the new title of the more venerable feast was changed to the “Solemnity of the Most Holy Body and Blood of Christ.” The new title is also faithful to the Church’s teaching that the faithful receive both the Body and Blood (and Soul and Divinity!) of the Lord when they receive Holy Communion under either species, that is, whether in the form (“accidents”) of bread or wine.
On June 30, 1849, Blessed Pope Pius IX, in exile from Rome due to an uprising there, received word that the revolutionaries had surrendered. In thanksgiving, and at the urging of the third superior general of the Missionaries of the Most Precious Blood who had accompanied the pontiff into exile, Bl. Pius IX soon thereafter established the feast on the first Sunday in July. Pope St. Pius X (1903-1914), during a reform of the liturgical calendar, moved the feast to July 1. Despite the more recent changes, already noted, there is a separate Votive Mass of the Most Precious Blood found in the current Roman Missal, which can be used throughout the year, in keeping with liturgical norms.
https://www.ewtn.com/catholicism/devotions/litany-of-the-most-precious-blood-of-jesus-248