Nope .. one will NOT be able to come to that conclusion after reading that "Doctrina Jacobi." .. In fact "Doctrina Jacobi." proves nothing except "Some one said something about some Prophet "....
Of course. That is why this text is used as evidence of the existence of the "prophet" :
Crone (
Hagarism) :
If we choose to start again [to remake the history of Islam], we begin with the Doctrina Jacobi, a Greek [...] but it does suggest that we have in the Doctrina a
stratum of belief older than the Islamic tradition itself. Of greater historical
significance is the fact that the Prophet is represented as alive at the time of the conquest of Palestine. [...] But the really startling thing about the Doctrina is its report that the Prophet was preaching the advent of 'the anointed one who is to come'.That is to say the core of the Prophet's message, in the earliest testimony available to us outside the Islamic tradition, appears as Judaic messianism.
Crone
"start again" nothing, as she takes for granted the existence of the "prophet" because of the Doctrina. She does not quote (first) other text. And she does it at the very commencement of
Hagarism (p.3)
How to
"start again" the history of Islam in taking for granted the existence of the producer of the Quranic text? It seems (to me...) not possible, or it is an
imposture. Because it means that it need a "prophet" to write it.