Leatherette volumes glued or sewn binding?

So I asked about this in the mystery thread but thought I would put it out there as a general question (forgive me if I’m asking too much): I was looking at some of my leatherette FL volumes (happen to all be from the mystery series) and it appears that the bindings might be glued instead of sewn...I can’t say for sure, but the pages don’t seem to be divided into signatures and the books definitely do not lie flat when opened.

Does anyone have any insight on this? Thanks!

>1 RRCBS: Franklin published a couple leatherette series unfortunately matching the leather edition in all content minus the ribbon. I was suckered into buying one volume by Walter Scott by probably an uninformed eBay seller. As I inspect it at the gutter level, I definitely see that it is sewn. Thus I suspect the Mystery series in faux leather is also sewn.

>1 RRCBS:
Most of my Mysteries collection are of the leatherette variety and, like you, I see no evidence of sewing. I’m pretty sure they are glued. A shame, but at least most of them are cheap!

This popular set is in serious need of updating. (Are you listening, Easton Press?) Many Great Mystery writers of the last 30 years are not represented.

>1 RRCBS:

I believe I have a 100 Greatest leatherette edition that is falling apart; if I find it, I'll dissect it and update you on whether the binding is sewn or glued.

>1 RRCBS:

The other night I finally found and dissected my leatherette copy of Gargantua and Pantagruel. I can confirm that the binding is in fact glued and not sewn. However, the glue that is used is fairly strong.

I know this thread is old but in case people still come across this while looking for answers I thought I would note that the non-leather editions from the Masterpieces of Mystery series do in fact have sewn bindings, difficult though they are to see.