First, thank you to Ryan Conlon for finding the listing of this manuscript that I could not find in the catalogue of the Nepalese-German Manuscript Cataloging Project, and for providing a link to it. This is very helpful.

Next, as I suspected, there is only one old manuscript of the Sarvatathāgatatattvasaṃgraha, not two. Daisy Cheung made this clear in an off-list reply to me. Thank you to her for that. She then provided additional information about it:

"For a new description of the Sanskrit MS of the STTS available see Tanemura 2020: (75)ff. 

Tamenura, Ryugen 種村隆元. 2020. ‘Saravatathāgatatattvasaṃgrahaの説くāveśa儀礼—金剛界大マンダラ章「成就が生じるための印に関する智」校訂テキストおよび和訳注—’. 智山学報 69: 71–97. 

"Tanemura 2020 can be downloaded here:

https://www.jstage.jst.go.jp/article/chisangakuho/69/0/69_0071/_pdf/-char/ja

It made no sense to me that there would be two very old manuscripts of this text, both discovered independently in the same library, first by Tucci in 1932 and then by David Snellgrove and John Brough in 1956. That was one reason for my inquiry, the other being a wish to obtain scans of this manuscript. The description of this manuscript by Tucci as being in late Gupta characters, and the description of this manuscript by Horiuchi as being in Siddham characters, led de Jong in his review (cited in my opening post) to assume two different manuscripts.

It is now clear that the manuscript reproduced in facsimile by Lokesh Chandra and David Snellgrove in 1981 is the same as the manuscript that was microfilmed by the Nepal-German Manuscript Preservation Project listed at the link provided by Ryan Conlon. If no one has a scan of this manuscript, now almost impossible to obtain from Kathmandu, or even a scan of the 1981 published facsimile of it, I will try to scan this facsimile and post it.

Thanks and best regards,

David Reigle

Colorado, U.S.A.