IMSLP Forums

Though these are a5, I can see only four facsimile part books. Can anyone help with the missing part?
Thanks
Robert

Probably the part of Altus 2 (most likely) is no more extant or, at least, has not been found until now. You can see the RISM description here.

Regards,

Link for RISM says "invalid". I did get to the site by clicking on A-Wn (scanner), and the site does mention the missing part.