In the "better late than never" department... I thought to revisit this thread to see if there had been any new developments. @Jleb1979, I was not familiar with the Sloat book, but after a bit of searching I was pleasantly surprised to find that as a member of the USSS, a PDF copy is available for download from the member site.
The quality of the illustrations in the PDF are not great, so it's impossible to tell if the vignette plate proof shows any semblance of the circles. While not a stamp of interest to me for in-depth research, I'm happy to share philatelic resources. @souldjer777, if you're still interested in pursuing this (or anyone else for that matter), I captured screenshots of the CE2 bibliography from the Sloat book which is likely to be a great starting point for further investigation. I have not reviewed any of these sources myself, but I can lead the horse to water, so to speak.
In cases like this, where a new discovery is suspected, it's absolutely a prerequisite to study all that's been previously written on the subject. Leave no stone unturned. Be assiduous and don't let your previously-drawn conclusions cloud your judgement (that can be harder than you might think). When researching something like this, it's essential that you be perfectly honest with yourself and your potential audience. Most importantly, have fun on the journey!