3c PAID in circle

Recently I have been come enamored with stampless letter that are marked "3c PAID" within a circle. This marking was used after June 30, 1851 when the basic paid rate was lowered to 3c. Since stamps became mandatory on January 1, 1856, the time frame for use was only 4-5 years. Here're 3 nicely cancelled examples:

Binghamton (Broome County) has been a post office since 1830. A nicely struck example on a very clean Ladies cover.

Cape Vincent (Jefferson County) has had 2 periods of operation: 1817 - 1861, and then again from 1861 to the current day. Again, a very nicely struck example on a watermarked type of paper.

Oramal was a post office in Allegany County in 1850, and again in 1852 - 1968.