Apart from "The RCA Victor Label Rings (1947 Standardizing Notice)" there is virtually nothing that I have as yet found that provides information regarding which pressing plant is represented by the various Bluebird label ring designs prior to the 1947 notice. I'm not sure whether John Bolig's Mainspring Press Bluebird Discography goes into this matter.
If anyone has information regarding this covering the 1930s and 40s variations, perhaps some kind of example template can be worked up or information posted to some of the individual entries which include a number of varying examples of a particular release. It would be deeply appreciated.
Unfortunately the images mentioned in the article (figure 1 etc.) are not there anymore but you may identify them on the other page.
There are some mistakes (or lack of clarity) in the article too. For example, after my own investigation the blue "staff label" was used much longer than November 1938, but only in Country, Race, and Rhythm and Blues series (which practically started at around B-7876 when the popular series jumped to B-10000). The last "staff label" in this series that I have found was Bluebird B-8242 from August 1939, higher numbers e.g. B-8249 have the "dog 3" label like the popular series.
Nothing about the pressing plants on these sources anyway. Actually I had difficulties to recognize the differences in the label variants A, B, and C that you presented for Bluebird B-10214, but I found them at last (broken lines, different line length).
Yes, I'm very familiar with the links provided. However, neither are very useful in attempting to identify the pressing plants connected with the specific label designs, as no information is offered.