The 18 star American flag was used between the years 1876 to 1890. During that time, in 1882, the China - Korea Treaty was signed.
The ChinaKorea Treaty of 1882 was negotiated between representatives of the Qing Dynasty and the Joseon Dynasty in October 1882. This agreement has been described as the Joseon-Qing Communication and Commerce Rules; and it has been called the Sino-Korean Regulations for Maritime and Overland Trade.
Maybe that is why the flag with rounded corners was posted.
Somehow, in all my research on the 18 star flag, I missed that. Do you have a link you could share? I'd appreciate it!
Niiiiiiice. excellent.