In the 1990s I catalogued a 13th-century Bible with varied and interesting indications of provenance, including an inscription "Zion MS. 2" on the first flyleaf, as shown above. Here it is in context:
The "Zion Collection" was the name given to a group of medieval manuscripts owned by The Endowment for Biblical Research, a subsidiary of the Christian Science Church in Boston, about which I was able to find out very little.
The collection was on long-term loan to Boston University in the 1980s, and the best source of information is the catalogue edited by Judith Oliver: Manuscripts Sacred and Secular from the Collections of the Endowment for Biblical Research and Boston University (Boston, 1985).
In 2008 I encountered another Zion Collection manuscript, so I contacted Judith Oliver for more information. She was able to tell me that Marguerite Smith, the librarian of the Endowment for Biblical Research (then called the Zion Research Foundation, located in Brookline, a suburb of Boston), is known to have bought manuscripts and leaves in London in the 1940s and 1950s. However, not long after the 1985 publication, the Church was in financial trouble and had to sell the collection. In 2015 I learned that the collection had been bought by an ex-employee of Goodspeed's (the Boston bookdealers) together with Bruce Ferrini, with various items then making their way to other dealers, private collectors, and into institutions.
Edit, 9 Oct 2021: This Sotheby's description states that Ferrini bought at least one Zion Collection item in May 1998
The current Bloomsbury Auctions catalogue provides information that is new to me. It includes a leaf from a Bible dispersed by Otto Ege, leaves of which were included as no. 13 in his portfolio of 'Fifty Original Leaves':
The Bloomsbury catalogue reveals that it was owned by Daniel Meyer Freidenberg (1923-2011), "with his pencil marks on reverse, recording this as his 'Zion 14'":this tribute in the New York Times, where he is described as a financier, collector, historian, philanthropist, and part-time Curator of Coins and Medals at the Jewish Museum in New York City from 1962-1982.
- Zion 1 (S&S no. 45): Paris-Bologna Bible. Sam Fogg, Illuminated Manuscripts (exh. cat., NYC, 1999), no. 6 (col. ills.) [added, 9 Aug. 2022:] now Toronto, Art Gallery of Ontario (AGOID.69293)
- Zion 3 (S&S no. 34): Paris Bible. Christie's, 20 November 2002, lot 17 (col. ills.)
- Zion 4 (S&S no. 21): Proverbs-Maccabees from a Bible. Private collection, London (previously Quaritch, Catalogue 1270: Bookhands of the Middle Ages, Part VI (2000), no. 20 (col. ill.); Charles Ryrie: his sale at Sotheby's New York, 6 December 2016, lot 7). Another portion of 125 leaves, Isaiah-II Maccabees, is Dallas, Harry Ransom Center, HRC 223. 
- Zion 5 (S&S no. 22): Wycliffite New Testament. Private Collection, Bel Air, CA
- Zion 6 (S&S no. 40): German pocket Bible. Sotheby's, 1 December 1998, lot 73 (ill.)
- Zion 10 S&S no. 91): Book of Hours, Use of Rennes. Bibliothèque municipale, Rennes (acquired from Les Enluminures in 1998)
- Zion 13 (S&S no. 86) The Felbrigg Hours. Huntington Library, HM 58285 (acquired from Sam Fogg in 1999) 
- Zion 86 (S&S no. 63): Leaf of the Beauvais Missal. Whereabouts unknown ...