Furthermore, it is generally known that he was 'chosen to represent Sorin OTOMO', but the Kao (written seal mark) on the letters written by Sorin to the Pope and so on were ones used in the earlier periods (1564 - 1572), and in contrast to the signature '普蘭師司怙' which was expressed by kanon (Han reading of Chinese characters) of Sorin's Christian name (Francisco), or '府蘭' (Furan) which was its abbreviation, both of which Sorin used at that time, the signature '不龍獅子虎' which was not seen in other letters was used in the letter to the Pope; the letter written by Sorin OTOMO that they were carrying has a high chance of being a forgery, and in fact, Sorin had no concern in youth dispatch since it was done under the leadership of ARIMA, OMURA, and Valignano, and there is a high possibility that it was not Sorin himself that appointed Mancio to be 'the representative of Sorin OTOMO', as is pointed out in the monograph and so on by Kiichi MATSUDA.
なお、「大友宗麟の名代として選ばれた」と一般に知られているが、ローマ教皇などに宛てられた宗麟の書状の花押が、古い時代（1564年～1572年頃）に使用されていたものであったり、署名が当時、宗麟が洗礼名（フランシスコ）を漢音で表した「普蘭師司怙」や、それを略した「府蘭」を用いていたのに対し、他の書状には見られない「不龍獅子虎」という署名を用いており、彼らが携帯していた大友宗麟の書状は偽作である可能性が高く、実際には宗麟は少年団派遣を関知しておらず、有馬氏・大村氏・ヴァリニャーノが主導となって行ったものであり、「大友宗麟の名代」として彼を任命したのは、宗麟本人では無い可能性が高い事が松田毅一氏の論文などで指摘されている。