What are the differences between the methods of reading al-Susi from Abu Amr, and what is the reason for the difference in affirming the extra ya' or not, even though the reciter is one?

The difference in reading methods (turuq) from a single narrator (rawi) is natural. A sheikh might teach his students with two different variations, as occurred with Al-Azraq and Al-Isbahani from Warsh concerning the Qasr (shortening) and Madd (lengthening), and as occurred in the varying methods from Hafs regarding the inclusion or omission of the saktah (a slight pause). Al-Zarqani clarifies that this difference is called a "riwayah" (narration) and not an additional "qira'ah" (reading). Hafs once asked 'Asim about Abu Bakr's deviation from him, and 'Asim explained that he taught Hafs according to what he narrated from Abu 'Abd al-Rahman al-Sulami from 'Ali ibn Abi Talib, whereas he taught Abu Bakr according to what he narrated from Zirr ibn Hubaysh from Ibn Mas'ud. Al-Dabba' mentioned that Ibn al-Jazari chose Hafs's narration from several methods, such as the Tariq al-Fil, from various sources.