[Ali Imran]

During Muhammad's lifetime, the Injil was already in circulation, as he affirmed its existence...This suggests that many people were reading it at that time. 

However, Moslems later claim that the Injil was lost. This presents a dilemma...if the Injil was indeed lost, does that mean all the Christians lost it as well? And if that's the case, how do historians not have any records of it?

 It seems unlikely and quite questionable to suggest that the Injil was completely lost without any trace.

Again. Let me remind you. What you have, the Gospels, all of them, are not the Injeel. They are the writings of unknown authors who wrote down their take on what they thought happened and the words of Jesus that were orally transmitted over a few decades.

So no, you cannot say what they have in the 7th century was the Injeel.