1426 8c Missouri Color Registration Circles

Flipping through some old postage to use, I found this partial plate block of 1426 8c Missouri. The selvage's color registration via yellow circles looked unfamiliar, and I am unable to think of another issue that employed it. I do not have plate blocks of all issues of that era to check. Instead of circles, more familiar is a row of colored boxes. Did any other issues employ circles like 1426?

I rechecked my plate blocks of that era and could not find a single other example of color registration circles in the selvage. Instead of circles, lines and boxes are common. Even the full plate block of the same Missouri issue lacks them as seen in this scan. It could be the circles are found in a different part of the selvage, or maybe only a portion of the Missouri printing has them.

Perf10,

I found a note following the listing for 1426 in Scott Specialized. More info available there. There can be "bars, dashes, or dots" in the margin. My plate block has dots. Now I need two more plate blocks!

Jr. Ratfish, thanks for looking it up. I wonder if bars vs. dots vs lines merely depends on plate position (UL, UR, LL, LR). Maybe a given full sheet has all three margin markings, but a pane has only one of those three?

I think it is based upon plate number, one plate number group has the circles and the other the marks (based upon looking at a number of full sheets online).
Don

I have both upper left plate blocks of 12 (#32708-32713 and #32702-32707)with dot registration marks and both lower left with double skewed lines. I don't have any with bars. None of my four right side plate blocks have registration marks.

Interesting, BaldEagle. There might be enough registration mark varieties for someone to write a book. I flipped through a bunch of plate strips I'd previously forgotten I had. No registration circles, but plenty of skewed lines and boxes, which leaves the ones on that Missouri issue as unique. IIRC that was the first commemorative at the then-new 8 cent rate.

Another unique color registration style I found is on the 25c Idaho issue 2439 that employs filled triangles, as shown.