That salt-box on the back was added in the 1990’s, to bring the overall depth of the barn to 30 feet. The original barn was only 20 feet deep, and that single seam you see on the back is where the original roof ends and the new extension was inserted under it. If you look at that second photo, you can see where the foundation starts for the addition, right at the grass line. They appear to have just bought more of the same roofing for the addition, and slid it up under the older roofing on the original structure, at that time.
No issues, and they have more than a foot of overlap, probably the result of using standard-length panels without cutting to fit. If doing new, I’d aim to just buy panels of the right length, or roll on-site.
My house roof is traditional raised seam, made with short panels, and the joints there are staggered. I think they’re staked to the underlayment at one end only, so the other end (and the joints) can float with thermal expansion.