Finding the answer I knew all along

More than ten years ago I read an introduction to the history of English law.   The following passage stuck with me.

The earliest canonists held marriage to be effected by the physical union of man and woman in carnal copulation.  They became one fled by commixtio sexuum .  But, since copulation could occur outside marriage, a mental element was also necessary.  There had to be an agreement to marry.  According to Gratian (c. 1140) marriage began by agreement but became complete and indissoluble only when the agreement had been sanctioned by a Church ceremony and consummated in a physical union.  There immediately arose difficulties with this approach.  The requirement of formality tended to increase the subjection of young couples to pressure from parents and lords, while the notion that physical union was essential led to embarrassing theological questions about the marital status of Christ's parents.

J. H. Baker, An Introduction to English Legal History , fourth edition
 (London: Butterworths Tolley, 2002), part two, ch. 28, p.479.

If Mary was perpetually a virgin (CCC 496-501 esp. 499) then the ideal of the Holy Family (CCC 1655) becomes ever more remote. I had wondered how this problem was resolved or if it had simply been quietly dropped.

Then Edward Peters (often mentioned in these parts) posted A caution re reading Bergoglio as a proto-Francis. He discusses an earlier Pope who had been involved in the debate between agreement and consummation as making a marriage.

The great canonist Rolandus Bandinelli lent his prestige to the Bologna interpretation. Coupled with Gratian and Hugh of St. Victor, Bandinelli was a powerful proponent of the consummation=marriage school. True, Bandinelli seemed to shift more toward the consent=marriage school later in his career as canonist, but even upon being elected Alexander III in 1159, he still vacillated between the two theories, and not for some time did he finally side with the Parisian interpretation that consent makes marriage (while consummation adds a technical type of indissolubility). Thus, even though it disagreed with a position Bandinelli had earlier strongly defended, Alexander firmly gave the Church an insight into marriage from which she has never retreated. Moral of the story: Something about being pope forces men to approach issues not as intellectual exercises, both sides of which can be argued, but as articulations of the doctrines and disciplines of the universal Church. Rather more weighty. I am, therefore, much more interested in what Francis says and does as pope than I am interested in what Bergoglio said and did as a bishop or priest or (good grief) as a seminarian. [emphasis added.]

Gosh I thought. There's the answer. So I came to write this post and found the following  in Baker immediately after the passage cited above.

After grappling with such problems, Pope Alexander III introduced, in the late twelfth century, a more sophisticated doctrine of marriage.  Under the new rules, marriage could be contracted by consent alone, without any ecclesiastical ceremony, parental consent or physical consummation, provided the consent was notified in words of the present tense (sponsalia per verba de praesenti ).  Such a marriage was irregular, in so far as the parties could be compelled for the sake of order and decency to solemnise the marriage publicly at the door of a church, and punished for any sinful connection theymay have had befofre so doing.  Yet it was valid and, before consummation, created an indissoluble bond which would be upheld even in preference to a subsequent church marriage with a different spouse.

Baker, op. cit. , pp.479-480.

I must have been asleep when I read that bit.