Here's an alleged John Calvin fact:
"John Calvin: It has been said that John Calvin belonged to the second generation of the Reformers and certainly his theology of double predestination governed his views on Marian and all other Christian doctrine . Although Calvin was not as profuse in his praise of Mary as Martin Luther he did not deny her perpetual virginity. The term he used most commonly in referring to Mary was 'Holy Virgin'."
This is another quote from the propaganda piece, The Protestant Reformers on Mary. This article states, "...the Marian teachings and preachings of the Reformers have been 'covered up' by their most zealous followers - with damaging theological and practical consequences." The quote from Calvin is supposed to suggest that Calvin most often called Mary, "Holy Virgin" while later Protestants do not. Keep in mind, "Holy Virgin" does not mean Calvin held to the immaculate conception (he did not). The phrase was simply a common way to refer to Mary.
Since no documentation is given, I'm not sure exactly where this fact came from. It's possible it came from David F. Wright (ed.), Chosen By God, Mary in Evangelical Perspective (London: Marshall Pickering, 1989), p. 175 via a Roman apologist like Peter Stravinskas. Wright states,
Calvin insists that Mary 'cherished the Son of God as much in her heart through faith as in her womb by conception... Mary's happiness in bearing Christ in her womb is not the fist thing — that honour actually is second in degree to [her] rebirth into newness of life by the Spirit of Christ' She was pronounced blessed in believing. 'It is quite absurd to teach tat we are to seek from her anything which she receives otherwise than we do ourselves.' Calvin commonly speaks of Mary as 'the holy Virgin' (and rarely simply as 'Mary' preferring 'the Virgin' etc), and also reasons that 'no great effort is required from us to clear her from all fault' when her response to Gabriel 'How will this be?' (Luke 1:34), appears to put a false limit on God's power. But even if Calvin rarely depicts Mary expressly as a sinner, he objected to her specific exclusion from the reach of original sin by the Council of Trent. he also argued that the Purification of Mary and Joseph in the temple (Luke 2:22-4) was necessitated by the universality of original sin — although even here his language is general rather than particular in its reference. Zwingli likewise often called Mary 'pure, holy, spotless', without offering an unambiguous commitment to either her immaculate conception or her sinlessness.
It appears to me that this comment from Wright that Calvin commonly speaks of Mary as the "Holy Virgin" turned into Calvin most commonly refers to Mary as the "Holy Virgin" at the hands of a Roman Catholic defender. I assume it's within the realm of possibility that someone has gone through Calvin's writings and kept score, but I doubt that any of the current Roman defenders have done so. While not meant to be conclusive, I did a basic search for the term "Holy Virgin" in my Ages Software, The Comprehensive John Calvin Collection. I counted approximately 30 instances of the phrase. When I searched for the term "Mary" (taking into consideration the various women named Mary in the Bible), I gave up counting, because the name was used so frequently. Unless the English translators of Calvin's writings have inserted the name "Mary" where it says in the original "Virgin" or "Holy Virgin," it appears to me David Wright is in error when he says Calvin rarely uses "Mary" preferring "the Holy Virgin" or "the Virgin."