Pope Gregory and Deuterocanonicals

In Moral on the Book of Job, Pope Gregory the Great (whether he wrote this book before or during his papacy, I don't know) quotes Sirach several times. Protestants are fond of using the Maccabee reference that it is "not canonical," what he meant by that is debated, but we can look at him quote other books:

That the acuteness of wisdom is designated by the ‘sun,’ is said also in the way of comparison by Solomon; A wise man continueth as the sun, a fool changeth as the moon. [Ecclesiasticus/Sirach 27:11] What then is pointed out in this place by the rays of the sun, but the acuteness of wise men?--Volume III, Part 6, Book XXXIV, Paragraph 25

And the love of our neighbour is carried down into two precepts, since on the one hand it is said by a certain righteous man, Do that to no man which thou hatest. [Tobit 4:15]  And on the other ‘Truth’ saith by Himself, Therefore all things whatsoever ye would that men should do to you, do ye even so to them. [Mat. 7:12]--Volume I, Part 2, Book X, Paragraph 8

In Sacred Writ ‘woman’ is taken either for the sex, or else for ‘frailty.’  For the ‘sex,’ as where it is written, God sent forth His Son, made of a woman, made under the Law [Gal. 4, 4].  But for frailty, as where it is said by the Wise Man, Better is the iniquity of a man than a woman doing well. [Ecclus./Sirach 42:14]  For ‘a man’ is the term for every strongminded and discreet person, but ‘a woman’ is understood of the weak or indiscreet mind.  And it often happens that even the discreet person suddenly falls into a fault, and that another weak and indiscreet man exhibits good practice.  But he that is weak and indiscreet is sometimes lifted up the more on the score of what he has done well, and falls the worse into sin; but the discreet person even from that which he sees that he has done amiss, takes occasion to recall himself with closer application to the rule of strictness, and advances the further in righteousness from the same act, whereby he seemed to have fallen from righteousness for a time.  In which respect it is rightly said, Better is the iniquity of a man than a woman doing well; in that sometimes the very fault of the strong becomes occasion of virtue, and the virtue of the weak occasion of sin. --Volume 2, Part 3, Book XI, Paragraph 65

Since according to the voice of Truth, Because iniquity shall abound, the love of many shall wax cold. [Matt. 24, 2]  He, then, who hath not warmth of the heart in the love of God, and yet keepeth not the life, which he loves, assuredly he ‘fleeth like a shadow.’  Hence it is well written concerning him, that he hath followed a shadow. [Sirach 34:2]  Now it is well said, and never continueth in the same state.--Volume II Part III, Book XI, Paragraph 88

Outside of Moralia, we see him also quoting Tobit and Sirach:

Lest they should give something, however little to those on whom they ought to bestow nothing at all, let them hear what is written, Give to the good man, and receive not a sinner: do well to him that is lowly, and give not to the ungodly [Sirach 12:4]. And again, Set out your bread and wine on the burial of the just, but eat and drink not thereof with sinners [Tobit 4:17].--Pastoral Rule (Book III)