This topic needs to be renamed if you want it to be about all plate varieties and not just the one in the initial title.
Also, if one wants to dig deep, this is where to start: Encyclopedia of Plate Varieties US Bureau-Printed Postage by Loran C French (1979)
It shows up for sale regularly but the three on eBay
right now are at nosebleed prices ($150+/-) unless the book suddenly jumped in value when not looking. $30-40 is more inline with what I have seen in person.
The 30 cent is not a "broken circle", it is a major double transfer.
Well, revcollector, that is why I wrote under the photo:
Double transfer gives look of broken areas.
If I had a photo I would post it but way back when I picked up my on cover example for a couple of bucks (yes well under $10) at PENPEX in Redwood City California.
However, I don't remember if cover is the DT left
, 14438 LR 79, unpriced mint, used or on cover; or, the one shown above which is right
, 16065 UR 52 which catalogs as $450.00 mint and unpriced used or on cover.
Edited for spelling, punctuation and pricing information.