I saw this binding in the Stiftsbibliothek St Gallen earlier this year with a type of cover that I have never seen before. It is made up from two pieces of manuscript waste (written locally, 11th or 12th century), one on each side, which overlap on the spine, to which they are adhered. The spine edges of both pieces have slots cut into them to fit on each side of the sewing supports, the slips of which are laced though the sides and trapped by the pastedowns. I am thinking of calling the cover type a ‘laced comb cover’, but has anyone seen another? The book inside is: Historia dess leidens und stärbens, Konstanz: [Balthasar Romätsch],1545 (Stiftsbiblothek St Gallen, EE r V 26.1). The library has kindly given us permission to reproduce these images.
Comb guard spine linings
I think what you have described is what I call a 'comb guard spine lining', in which the inner end of each slot cut across the comb linings is left with a small tab which is folded around the spine edges of the first or last gatherings (not tucked back through them but between the outermost and next gathering at each end - comb linings always come in pairs) to reinforce the sewing stations. This seems to be a particularly German type of lining, and possibly from southern Germany only. It is possible for the joints of comb linings to extend across the full width of the bookblock (some French binders made so-called 'doublures' of tanned goatskin as 'extended comb linings'), and that is why I suggested the name 'laced comb cover' for the St Gallen binding .
I have not seen an example like this in our collection of 140 + books bound in ms waste. I have seen an example of parchment ms waste used as spine lining and slots cut from around the supports and then the slips folded back and tucked back through the first gathering.