Companion Pair Kutani Plates. (different marks though).

I bought these from a dealer's home outside Austin years ago. I must have seen an ad in the paper otherwise I would have never gone down a dirt road in search of these.

The thing that has puzzled me is even though they look pretty much a pair at first glance, they are slightly different. One is slightly more faded in the blue pattern around the edge. The mark on that one is the square mark. The front designs are pretty much identical considering they are hand painted.

The other plate has a slightly darker pattern around the edge on the front. It is more of a cobalt blue. The difference is not really noticeable unless you are looking for it. The mark on the back of this one is the string of characters. Why the complete difference in the marks?
It the more faded plate older?

Thanks for any info. I know marks can be spurious at best, but I know nothing about marks.