Coming from a Christian perspective, I can tell you that the general principle of prophetic succession is such that once a prophet arrives, his claim is made to rest on the authority of previous prophets.
Since Mohammed was, by all accounts, the last of the prophets, it would have been remarkable if he had been named in prior books. To give some idea of the time frames involved -
- The Torah was written ~1000BC to ~450BC
- The New Testament (the Injil) was written between 52 AD and ~ 95 AD
- Mohammed lived from ~572AD to 632AD
It is difficult to imagine a nonsensical datum existing for over 1600 years in any book, let alone a holy one.
In Christian and Jewish traditions, there is no example of a prophet being named prior to his appointment. Even Jesus, whom Christians view as both a prophet and as "the Messiah," the concept of Messiah is traced historically, but the name of Jesus does not appear until the angel Gabriel announces to Mariam. As another example, John the Baptist is often conflated with Elijah - a prophet who preceeded John the Baptist by 600 years - but again John the Baptist is later associated, not named.
The most famous example of the Prophet Muhammad being "named" in "Scripture" comes from "The Gospel of Barnabas," a work not recognized by Christians or Jews as sacred. The earliest mention of text is contemporaneous with the Prophet, and is thus both well after Christians believe the canon to be closed and in any event not inspired at all.