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Many of the Marian doctrines were not officially declared, though they had been universally held.

For example, Perpetual Virginity was defended, in at least in 383 AD (http://www.newadvent.org/fathers/3007.htm) a long, but interesting read.

From antiquity:

Irenaeus (c.130 – c.202) taught perpetual virginity, along with other Marian themes.[32] However, wider support for the doctrine began to appear within the next century.

By the 4th century, the doctrine of perpetual virginity had been well attested.[43] For example, references can be found in the 3rd century writings of Hippolytus of Rome, who called Mary “the tabernacle exempt from defilement and corruption,” [44] and the 4th century works of Athanasius,[45] Epiphanius,[46] Hilary,[47] Didymus,[48] Ambrose,[49] Jerome,[50] and Siricius[51] continued the attestations to perpetual virginity – a trend that gathered pace in the next century.[4][5]

Then at the Reformation:

Martin Luther believed that Mary did not have other children and did not have any marital relations with Joseph. The Latin text of the 1537 Smalcald Articles, written by Martin Luther, used the term “Ever Virgin” to refer to Mary.[69] The perpetual virginity of Mary was Luther’s lifelong belief, even after he rejected other Marian doctrines.[69][72][73]

Huldrych Zwingli directly supported perpetual virginity and wrote: “I firmly believe that [Mary], ... forever remained a pure, intact Virgin.”[74] Like Zwingli, the English reformers also supported the concept of perpetual virginity, but often varied on their reasons for the support.[70] Luther and Zwingli’s support of perpetual virginity was endorsed by Heinrich Bullinger and was included in the 1566 Second Helvetic Confession.[75]

The Anglican reformers of the 16th and 17th century supported perpetual virginity “on the basis of ancient Christian authority”.[69] In the 18th century, John Wesley, one of the founders of Methodism, also supported the doctrine and wrote that: “... born of the blessed Virgin Mary, who, as well after as before she brought Him forth, continued a pure and unspotted virgin.”[69][78][79]

Regarding the Immaculate Conception of Mary: Although the belief that Mary was sinless and conceived immaculate has been widely held since Late Antiquity, the doctrine was not dogmatically defined until 1854, by Pope Pius IX in his papal bull Ineffabilis Deus.

Finally, the Assumption of Mary was declared in 1950: Although the Assumption (Latin: assumptio, “a taking”) was only relatively recently defined as infallible dogma by the Catholic Church, and in spite of a statement by Saint Epiphanius of Salamis in AD 377 that no one knew whether Mary had died or not,[7] apocryphal accounts of the assumption of Mary into heaven have circulated since at least the 4th century. The Catholic Church itself interprets chapter 12 of the Book of Revelation as referring to it.[8] The earliest known narrative is the so-called Liber Requiei Mariae (The Book of Mary’s Repose), which survives intact only in an Ethiopic translation.[9][10][11] Probably composed by the 4th century, this Christian apocryphal narrative may be as early as the 3rd century. Also quite early are the very different traditions of the “Six Books” Dormition narratives.[12] The earliest versions of this apocryphon are preserved by several Syriac manuscripts of the 5th and 6th centuries, although the text itself probably belongs to the 4th century.[13][14][15]

So, Marian doctrines go way, way back.