In the opening pages of "Masu Kagami," which is almost certain to have been written in the first half of the period of (Japanese) Northern and Southern Courts (around the middle of the 14th century), the author made a definite statement that "Masu Kagami" was a sequel to "Iya Yotsugi," which naturally suggests that "Iya Yotsugi" had already existed in that time.
南北朝時代_(日本)前期（14世紀中頃）に書かれた事がほぼ確実とされている『増鏡』の冒頭にも『増鏡』が『弥世継』の続きである事が明言されており、当然にこの時代には『弥世継』が存在していた事になる。