Analysis of information sources in references of the Wikipedia article "États ayant versé un tribut à la Chine impériale" in French language version.
« Between 1392 and 1450, the Choson court dispatched 391 envoys to China: on average, seven each year. »
« thus, between 1637 and 1881, Korea sent 435 special embassies to the Qing court, or an average of almost 1.5 embassies per year. »
« Joseon requested to send a tribute "thrice each year" or "four times per year" instead and achieved it. »
« The tribute taken to Beijing three or four times a year during most of the Joseon period provides an interesting insight into Korean products at this time. »