Why is the story of Joachim and Anne considered true in tradition but mentioned only in apocryphal works? Recently I have been reading about different Christian traditions that aren't neccesarily written in scripture but have been accepted by the RCC (and sometimes Orthodox Church) as tradition and true. The story of St. Joachim and St. Anne is only mentioned in the apocryphal Protoevangilium of James. How can the story of Joachim and Anna be true if it is written in a book that was made apocryphal by the church? Are there any other early sources that also affirm what the Gospel of James says about the parents of Mary or is that the only one?
Why is the story of Joachim and Anne considered true in tradition but mentioned only in apocryphal works?
The Apocrypha are not considered inspired revelation from God. But that does not mean that certain works may contain some truths within them. The Scriptures can not err, but the Apocrypha may hold some errs. This is where tradition comes in: it’s tradition!

Jesus, Disciples Never Quoted from Apocrypha: Jesus Christ and his inspired New Testament penmen quoted from, or alluded to, the writings and events of the Old Testament profusely. In fact, there are one thousand quotations or allusions from thirty-five of the thirty-nine Old Testament books are found in the New Testament record.
And yet, significantly, not once are any of these apocryphal books quoted or even explicitly referred to by the Lord or by any New Testament writer.
Noted scholar Emile Schurer argued that this is really remarkable since most of the New Testament habitually quoted from the LXX (1894, 99).

Despite the fact that New Testament writers quote largely from the Septuagint rather than from the Hebrew Old Testament, there is not a single clear-cut case of a citation from any of the fourteen apocryphal books .... The most that can be said is that the New Testament writers show acquaintance with these fourteen books and perhaps allude to them indirectly, but in no case do they quote them as inspired Scripture or cite them as authority (Unger 1951, 101).

Apocryphal Books Do Not Claim Inspiration: It must be observed that the apocryphal books, unlike the canonical books of the Old Testament, make no direct claims of being inspired of God.
Not once is there a, “thus says the Lord,” or language like, “the word of the Lord came unto me, saying ...” In fact, some of the documents actually confess non-inspiration! In the prologue of Ecclesiasticus, the writer states:

“Ye are intreated therefore to read with favour and attention, and to pardon us, if in any parts of what we have laboured to interpret, we may seem to fail in some of the phrases.”


It seems that the Golden Legend fixed this tradition in the minds of those who accept the story.
The Catholic Encyclopedia has this to say about St. Joachim and St. Anne:

All our information concerning the names and lives of Sts. Joachim and Anne, the parents of Mary, is derived from apocryphal literature, the Gospel of the Nativity of Mary, the Gospel of Pseudo-Matthew and the Protoevangelium of James. Though the earliest form of the latter, on which directly or indirectly the other two seem to be based, goes back to about A.D. 150, we can hardly accept as beyond doubt its various statements on its sole authority. In the Orient the Protoevangelium had great authority and portions of it were read on the feasts of Mary by the Greeks, Syrians, Copts, and Arabians. In the Occident, however, it was rejected by the Fathers of the Church until its contents were incorporated by Jacobus de Voragine in his &quot;Golden Legend&quot; in the thirteenth century. From that time on the story of St. Anne spread over the West and was amply developed, until St. Anne became one of the most popular saints also of the Latin Church.
The Protoevangelium gives the following account: In Nazareth there lived a rich and pious couple, Joachim and Hannah. They were childless. When on a feast day Joachim presented himself to offer sacrifice in the temple, he was repulsed by a certain Ruben, under the pretext that men without offspring were unworthy to be admitted. Whereupon Joachim, bowed down with grief, did not return home, but went into the mountains to make his plaint to God in solitude. Also Hannah, having learned the reason of the prolonged absence of her husband, cried to the Lord to take away from her the curse of sterility, promising to dedicate her child to the service of God. Their prayers were heard; an angel came to Hannah and said: &quot;Hannah, the Lord has looked upon thy tears; thou shalt conceive and give birth and the fruit of thy womb shall be blessed by all the world&quot;. The angel made the same promise to Joachim, who returned to his wife. Hannah gave birth to a daughter whom she called Miriam (Mary). Since this story is apparently a reproduction of the biblical account of the conception of Samuel, whose mother was also called Hannah, even the name of the mother of Mary seems to be doubtful.
The Greek Menaea (25 July) call the parents of St. Anne Mathan and Maria, and relate that Salome and Elizabeth, the mother of St. John the Baptist, were daughters of two sisters of St. Anne. According to Ephiphanius it was maintained even in the fourth century by some enthusiasts that St. Anne conceived without the action of man. This error was revived in the West in the fifteenth century. (Anna concepit per osculum Joachimi.) In 1677 the Holy See condemned the error of Imperiali who taught that St. Anne in the conception and birth of Mary remained virgin (Benedict XIV, De Festis, II, 9). In the Orient the cult of St. Anne can be traced to the fourth century. Justinian I (d. 565) had a church dedicated to her. The canon of the Greek Office of St. Anne was composed by St. Theophanes (d. 817), but older parts of the Office are ascribed to Anatolius of Byzantium (d. 458). Her feast is celebrated in the East on the 25th day of July, which may be the day of the dedication of her first church at Constantinople or the anniversary of the arrival of her supposed relics in Constantinople (710). It is found in the oldest liturgical document of the Greek Church, the Calendar of Constantinople (first half of the eighth century). The Greeks keep a collective feast of St. Joachim and St. Anne on the 9th of September. In the Latin Church St. Anne was not venerated, except, perhaps, in the south of France, before the thirteenth century. Her picture, painted in the eighth century, which was found lately in the church of Santa Maria Antiqua in Rome, owes its origin to Byzantine influence. Her feast, under the influence of the &quot;Golden Legend&quot;, is first found (26 July) in the thirteenth century, e.g. at Douai (in 1291), where a foot of St. Anne was venerated (feast of translation, 16 September). It was introduced in England by Urban VI, 21 November, 1378, from which time it spread all over the Western Church. It was extended to the universal Latin Church in 1584.