I think it's possible there was a Syriac translation of the Gospels that could have mentioned the "Ahmad" in the Qur'an that was lost... or yet to be discovered.
I would really feel it is inappropriate to reference a site like "answeringinfidels" or referencing them on a Comparative Religion Forum..
THe following is based on notes by A. Guillaume translator of the Inb Ishaq "Sirat Rasul Allah" some of which can be found on p. 104:
In the Sira, the biography of the Prophet, written by Ibn Ishaq, we have a quote from the Gospel of St. John that is relevant for us:
“Among the things which have reached me about what Jesus the Son of Mary stated in the Gospel which he received from God for the followers of the Gospel, in applying a term to describe the apostle of God, is the following. It is extracted from what John [Yuhannis] the apostle set down for them when he wrote the Gospel for them from the Testamant of Jesus Son of Mary: ‘He that hateth me hateth the Lord. And if I had not done in their presence works which none other before me did, they had not had sin: but from now they are puffed up with pride and think that they will overcome me and also the Lord. But the word that is in the Law must be fulfilled, 'They hated me without a cause' (ie. without reason). But when the Comforter [Munahhemana] has come whom God will send to you from the Lord's presence, and the spirit of truth [ruhu`l-qist] which will have gone forth from the Lord's presence he (shall bear) witness of me and ye also, because ye have been with me from the beginning. I have spoken unto you about this that you should not be in doubt.’
“The Munahhemana (God bless and preserve him!) in Syriac is Muhammad; in Greek he is the Paraclete [Albaraqlitis ]” [22]
Alfred Guillaume [23] has very convincingly argued that Ibn Ishaq must have had access to a Palestinian Syriac Lectionary of the Gospels:
“It will be apparent to the reader that Ibn Ishaq is quoting from some Semitic version of the Gospels, otherwise the significant word munahhemana could not have found a place there. This word is not to be found in the Peshitta version [Syriac version of the Bible], and in the Eastern patristic literature…it is applied to our Lord Himself. Furthermore the Peshitta, Old Syriac, and Philoxenian versions all write the name of John in the form Yuhanan, not in the Greek form Yuhannis found in the Arabic text. Accordingly to find a text of the Gospels from which Ibn Ishaq could have drawn his quotation we must look for a version which differs from all others in displaying these characteristics. Such a text is the Palestinian Syriac Lectionary of the Gospels [24] which will conclusively prove that the Arabic writer had a Syriac text before him which he, or his informant, skilfully manipulated to provide the reading we have in the Sira.
“ …Apart from the spelling of the name Johannes …the renderings of Paracletus and Spiritus veritatis are crucial. It has long been recognized that the Palestinian Syriac Lectionary has been strongly influenced by Jewish Aramaic and nowhere is this more perceptible than in their rendering of Paraclete which the Syriac Versions and the Vulgate simply transliterate, preserving the original Greek term as the English Bible in some places. The word Paraclete has been 'naturalized' in Talmudic Literature and therefore it is strange that the Syriac translators of the Lectionary should have gone out of their way to introduce an entirely new rendering, which given its Hebrew meaning has, by a strange coincidence, the meaning 'Comforter' of the English Bible ….But in ordinary Syriac no such meaning is known. There menahhemana means ‘life-giver’ and especially one who raises from the dead, while nuhama stands for resurrection in John XI.24, 25. Obviously this cannot be the meaning of our Lord’s words in the passage before us. What is meant is one who consoles and comforts people for the loss of one dear to them, their advocate and strengthener, a meaning attested by numerous citations in Talmudic and Targumic dictionaries.
"Secondly for spiritus veritatis the best MSS of Ibn Ishaq have ruhu `l-qist, which later writers have gratuitously altered to ruhu `l-quds. But qist is not truth, but rather 'equity' or 'justice'. Whence, then, came the word? There is no authority for it in the Old Syriac or Peshitta which read correctly sherara. Again the answer is to be found in the Lectionary which has ruh d`qushta, the correct meaning in Jewish Aramaic." [25]
It is worth noting that Schulthess in his Palestinian Syriac Lexicon gives the secondary meaning of “to Console, comfort” for nHem, naHHem. [26]
Guillaume`s discovery is of enormous importance, since it lends credence to Christoph Luxenberg’s theory that the Koran must have emerged out of a Syriac Christian milieu. Guillaume has conclusively shown that Ibn Ishaq must have had access and recourse to Syriac Christian texts.
Koranic Criticism: 700 C.E. to 825 C.E. > Ibn Warraq