Hey there Josh,
The 811 with a "skinny stripe" down the back is an aesthetic touch that differentiates it from its brethren without the strip. Bottom line: they are
two-piece backs.
Disclaimer: I've not seen an 800 with said appointment, personally. But there have been Taylors in the past with such adornments, whether two-piece or three piece, where the latter is typically a wedge shape to make it look "better" for those so inclined. The point is Taylor has
never made a one-piece back for the
solid-wood guitars --300 series upward-- that I have known of or seen, not ever. Either they have a unicorn out there, or what you are seeing as "one-piece" is likely a well-matched two-piece back (often called
bookmatched) which is not at all uncommon, particularly in some woods where its grain tends to not be so "dramatic" so as to appear like one slab. Mahogany comes to mind. Fwiw, I've seen many a Les Paul whose mahogany body reveals a back that looks like one piece, but under a very close eye you can see the seam. For example, anyway.
EDIT: I just now googled up some images of 811 backs and sure enough, there are several examples there of rw backs that have very straight grain and uniform hue that can easily be mistaken as one piece. And I saw one from Zounds that has the stripe you mention. Imagine
not building in the stripe and that exact wood example could easily look like a single piece:
https://www.zzounds.com/item--TAYGT811Bottom line: these are aesthetic considerations and have no effect on tone or structure, only one's perception of "beauty." Hope this helps you a bit.

Edward