Another dumb question.

15th (16th) C.
I am told the wooden core of a scabbard, after glueing, is wrapped in a piece of strong linnen with hide glue. Some say a large single piece with ends meeting at the centre back is authentic, unlike winding thinn strips around it. Others tell me the other way round.
What precious few pictures I have collected so far of original scabbards, that allow seeing the construction, all seem to have the leather directly over the wood, no linnen inbetween.

18th C

One primary text source makes no mention of wrapping the wooden core in anything. A 1945 secondary source, without giving the original source, claims the scabbard is 'Served over' i.e. tightly wrapped, in fine linnen thread, then sizing (which I take to mean glue) is applied and when dry sanded/smoothed a bit.

I don't know how reliable that secondary source is, and smallsword scabbards are surprisingly rare survivors, museums descriptions of materials used are usually woefully incomplete and pictures showing anything that could reveal the construction are rarer than unicorns.
I have 1 (-one-) picture of a crumbling small sword scabbard, that shows that it has a wooden core, vellum cover and...nothing else?

It seems decent books, publications or just photos and descriptions of original scabbards of whatever century are extremely elusive!

I have been trying to gather information on period scabbards and suspensions as well and it is indeed as rare as a unicorn. I have read that 13th and 14th century scabbards were often covered in fabric as the final assembly and no leather covering. Have you come across that anywhere in you search?

Not really.

I am really only at the very beginning of this whole thing, and mostly looking for very late stuff.

still I am already struck by the dearth of publications or anything solid on scabbards, no matter the era...

It's not that surprising. After all, scabbards were (and are) usually made of perishable materials, and we can rarely see much detail about their internal construction except if the scabbard has been damaged or destroyed (while scabbards in such damaged condition would have been very likely to be discarded rather than preserved).