Hi bobbie,
There are benefits for both sides. Gluing and finishing a mattress can make a little more “stable” mattress that is tighter around the foam and can shift or bunch a little less and the layers act a little less independently which can create a little firmer feeling. The sides of the cover can also be re-inforced and it may be a little stronger than a zipper cover. It may slightly increase durability “in theory” although it’s questionable whether the difference with a material like latex would be enough to make a significant difference in real life. In some cases a local manufacturer can open up the mattress and change out a layer if necessary if they leave the layers loose or at least wait with gluing until the final layering is confirmed. In some cases even the quilting and ticking can be glued to keep them from stretching over time.
Some types of mattress designs also have multiple thinner layers that use materials and components that are less “sticky” and more prone to bunching or shifting and need to be attached to each other or to an innerspring underneath them to prevent them from shifting or bunching and for these types of mattress a tape edged cover along with other construction methods such as using hog rings to tightly attach the layers to an innerspring or tufting would also be necessary for the mattress to keep its shape over time.
Component mattresses also tend to have standardized components and layer thicknesses so that individual layers or components can be more easily replaced or customized with different firmness levels and still fit inside the same thickness zip cover so there are some limitations on the number of designs and layer thicknesses that are available while finished mattresses where the layers and components inside are attached to each other have a much wider range of different design possibilities.
A zip cover with loose layers provides options that allows a customer to “fine tune” the feel or pressure relief or support of the mattress by rearranging or exchanging layers layers either initially or down the road. It also allows a single layer to be replaced if one layer softens or wears out faster than the others or if your needs or preferences change over time so you can replace an individual layer without replacing the whole mattress. Separate layers also act a little more independently and will “act” a little softer although other factors (such as ILD or layer thickness) will affect this as well. “Component” mattresses of different types are becoming more popular because of the more flexible options they make available.
Latex is very sticky so loose layers tend to stay put and if for some reason they do shift over time or because you move the mattress or put it on its side it’s an easy process to unzip the cover and “wave” the layers back into position.
If I was buying a finished mattress with no zipper I would probably choose to have them glued and if I was buying a mattress with a zip cover and I had access to the individual layers then I would choose to have them loose because of the advantages it offers.
I don’t think either is a “better or worse” choice but with a choice where everything else seemed equal I would personally lean towards more options vs the benefits that can come from gluing or finishing a mattress but of course each person may have a different preference. There is more about a finished mattress that is tape edged vs a component mattress with a zip cover in post #2 here.
I don’t believe that 'theory at a distance" is as accurate as your own personal testing so I tend to limit my comments to any “risk” or “weak links” that I see and I don’t see any in the specs you mentioned. If your more “objective” testing and best judgement in consultation with each manufacturer confirms it, then they seem very reasonable to me. They are a little thicker than the 10000 “organic” series (9.5" vs 9" of latex) and the layer thicknesses and ILD’s and components (like the quilting layer) are different so they would have differences in feel and performance to some degree (depending on your choices) but they are close enough in spite of the differences to make a reasonable or meaningful comparison between them.
The law label probably wouldn’t differentiate more than saying latex so it really boils down to the reputation and integrity of the manufacturer and trusting your best judgement about the truth of what they are telling you.
You are down to some “good options” which of course is always the best place to be 
Phoenix