根據《續高僧傳 ‧釋法上傳》的記載，法上在東魏、北齊兩代擔任沙門統、沙門大統，統領僧團歷時近四十年，在當時可謂僧團第一人。 538年在其師慧光過世後，最早在這一年法上擔任沙門統， 577年北周滅北齊，法上應是在這一年卸任，統領僧團近四十年則約為 538-577年。
2007年鄴城出土一方墓誌銘，田熊信之透過解讀該銘文，發表〈大齊故昭玄沙門大統僧賢墓銘疏攷〉，提出僧賢的生卒為 505-570年，且約於北齊武成帝河清二年（ 563）時擔任沙門大統。又 1987年劉東光、陳光唐發表〈邯鄲鼓山水浴寺石窟調查報告〉，文中提到水浴寺石窟西窟前壁的供養人圖像旁有題記「昭玄大統定禪師供養佛」，西窟主壁有發願文「武平五年（ 574）甲午歲十月戊子朔」，時間為北齊後主時期。僧賢、定禪師擔任沙門大統的時間與法上擔任的時間重疊，表示北齊沙門大統的員額，在文宣帝過世後，自武成帝時期開始增加，但最多同一時期兩位，六世紀 60年代為法上、僧賢， 70年代則為法上、定禪師。
此一發展，與北朝僧官的兩個變化相應，一者層級增加，即最高層級的僧官由沙門統、都維那擴增為沙門大統、沙門統、都維那三級；二為員額的增多，北魏、東魏時，同時期僅一位沙門統，北齊文宣帝時沙門統員額增加，自武成帝時期開始沙門大統的員額也出現增加的現象，而至多同一時期兩位。

According to his biography in Continued Biographies of Eminent Monks (Xu Gaoseng Zhuan), Fashang was named Superior Administrator of Sangha and Great Superior Administrator of Sangha during the Eastern Wei and the Northern Qi dynasties, leading the entire monastic order in the north for nearly forty years. Fashang’s nomination can be dated back as early as 538 AD, the year his master Huiguang passed away. He likely left the position when the Northern Qi was conquered by the Northern Zhou, in 577.
An article by Takuma Nobuyuki, based on an epitaph excavated in Yecheng in 2007, examines an inscription that describes the life of a Great Superior Administrator named Sengxian in the Northern Qi dynasty. He argues that Sengxian’s dates of birth and death were 505 and 570 respectively, and that he was nominated as Great Superior Administrator by Emperor Wucheng in 563. A 1987 report by Liu Dongguang and Chen Guangtang uses inscriptions to identify a certain Ding Chan Master as Great Superior Administrator in 574. Thus the rule of Sengxian and Ding Chan Master as Great Superior Administrator of Sangha overlapped with that of Fashang. This means that from the reign of Emperor Wucheng, the number of Great Superior Administrator of Sangha increased, but with two at the most in the same period, with Fashang and Sengxian serving in the 560s, and Fashang and Ding Chan Master in the 570s.
This development corresponded to two changes in the system of official monks in the Northern Dynasties. First, the number of ranks increased. The highest level of the official monastic system changed from two positions, Superior Administrator of Sangha and duweina, to three positions, namely Great Superior Administrator of Sangha, Superior Administrator of Sangha, and duweina. Second, the number of posts increased from one Superior Administrator of Sangha in the Northern Wei and Eastern Wei dynasties to several in the period of Emperor Wenxuan of the Northern Qi dynasty. Also, the number of Great Superior Administrators of Sangha increased from the period of Emperor Wucheng.