The date (under the [liturgical year](https://en.wikipedia.org/wiki/Liturgical_year)) would be announced at each mass in Catholic areas throughout the medieval era in Europe.  So everyone would have a good general idea of dates. There is a nice picture of a liturgical calendar (used by priests in the 1200s) [here](https://en.wikipedia.org/wiki/Liturgical_year#/media/File:BritLibCottonCleoBIXLiturgicalCalOct.jpg).  The Catholic Encyclopedia has a long article on the history of the [Christian calendar](http://www.newadvent.org/cathen/03158a.htm).

To give an idea about how well the calendar was 'nailed down' even quite early, here is the list of dates (and events) from an English liturgical calendar from the 700s (around AD 702).  These dates would all have been announced to the townsfolk.

    JANUARY
    
    1 Circumcision 
    3 St. Genevieve of Paris 
    6 Epiphany 
    13 St. Hilary 
    14 St. Felix of Nola 
    17 St. Anthony, Hermit 
    18 St. Peter's Chair at Rome and the Assumption of Holy Mary 
    20 St. Sebastian
    21 St. Agnes (Virgin) 
    24 St. Babilas, Bishop and Martyr 
    25 Conversion of St. Paul at Damascus 
    29 St. Valerius, Bishop, and St. Lucy (Virgin) at Treves
    
    FEBRUARY
    
    1 St. Denis, St. Polycarp and St. Brigid (Virgin) 
    2 St. Symeon, Patriarch 
    5 St. Agatha 
    6 St. Amandus 
    16 St. Juliana 
    22 The Chair of Peter at Antioch
    
    MARCH
    
    1 Donatus 
    7 Perpetua and Felicitas 
    12 St. Gregory at Rome 
    17 St. Patrick, Bishop in Ireland 
    20 St. Cuthbert, Bishop 
    21 St. Benedict, Abbot 
    25 The Lord was crucified and St. James the brother of Our Lord 
    27 The Resurrection of Our Lord
    
    APRIL
    
    4 St. Ambrose 
    22 Philip, Apostle
    
    MAY
    
    1 St. Philip, Apostle 
    5 The Ascension of the Lord 
    7 The Invention of the Holy Cross 
    11 Pancratius, Martyr 
    14 Earliest date for Pentecost 
    31 St. Maximinius at Treves
    
    JUNE
    
    2 Erasmus, Martyr 
    8 Barnabas, Apostle 
    9 St. Columkill 
    22 James the son of Alpheus 
    24 Nativity of John the Baptist 
    29 Sts. Peter and Paul at Rome
    
    JULY
    
    15 St. James of Nisibis 
    26 St. James, Apostle, Brother of John 
    26 St. Symeon, Monk in Syria 
    29 St. Lupus
    
    AUGUST
    
    1 The Machabees, seven brothers with their mother 
    5 St. Oswald, King 
    6 St. Syxtus, Bishop 
    10 St. Laurence, Deacon 
    13 Hippolitus, Martyr 
    16 (Sic) [erasure] St. Mary 
    25 St. Bartholomew, Apostle 
    28 Augustine and Faustinus, Bishops 
    29 Martyrdom of St. John the Baptist 
    31 St. Paulinus, Bishop at Trier
    
    SEPTEMBER
    
    7 Sergius, Pope at Rome 
    9 (Sic) Nativity of St. Mary at Jerusalem 
    13 Cornelius and Cyprian 
    15 St. Euphemia, Martyr 
    19 Januarius. Martyr 
    21 Matthew, Apostle 
    22 Passion of St. Maurice 
    24 Conception of St. John the Baptist 
    27 Cosmas and Damian at Jerusalem 
    29 St. Michael, Archangel
    
    OCTOBER
    
    1 Remedius and Germanus 
    4 Sts. Heuwald and Hewald, Martyrs 
    14 Paulinus, Bishop in Canterbury 
    18 Luke, Evangelist 
    28 Simon and Jude, Apostles 
    31 St. Quintinus, Martyr
    
    NOVEMBER
    
    10 St. Leo, Pope 
    11 St. Martin, Bishop at Tours 
    22 St. Cecilia 
    23 Clement at Rome 
    24 Crisogonus 
    30 St. Andrew, Apostle
    DECEMBER
    
    10 St. Eulalia and seventy-five others 
    20 St. Ignatius, Bishop and Martyr 
    21 St. Thomas, Apostle in India 
    25 Nativity of Our Lord Jesus Christ 
    26 St. Stephen, Martyr 
    27 John, Apostle, and James, his brother 
    28 The Innocents 
    31 St. Silvester, Bishop