The text does not limit itself to the original coming --
Those verses are about as plain as any in the Bible. I don't see how any other interpretations can be wrung from those sentences. The "original coming" is clearly what is being discussed.
And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God, and this is that spirit of antichrist, whereof ye have heard that it should come; and even now already is it in the world." [I John 4:2,3] "Hereby know ye the Spirit of God: Every spirit that confesseth that Jesus Christ is come in the flesh is of God:
IOW, the verse tells us...
Here's how you know if a man is indwelled by the Holy Spirit. If a man professes that Jesus Christ has been born and stood among us as God and man, then he is a true believer. If a man denies that Jesus Christ, the Son of God, has been born and lived among us, then that person is actually denying the Holy Spirit (the unpardonable sin) and he is an anti-Christ.
I'm generally a KJV-only reader, but let's see what the NIV says...
This is how you can recognize the Spirit of God: Every spirit that acknowledges that Jesus Christ has come in the flesh is from God, but every spirit that does not acknowledge Jesus is not from God. This is the spirit of the antichrist, which you have heard is coming and even now is already in the world." -- 1 John 4:1-3"Dear friends, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world.
Not at all ambiguous in either version.