Don't agree with this,
we know the LORD has sealed his people on the foreheads at least one other time.
so why couldn't the mark of the beast been around then as well?
Because, like I already pointed out, it would contradict Revelation 16:2, therefore, making that verse untrue. The verse indicates that the vial is poured out on those with the mark. Kind of hard to do that if when someone has the mark it is not during the time of the vials of wrath. Let's also look at it from another perspective.
Revelation 13:1 And I stood upon the sand of the sea, and saw
a beast rise up out of the sea, having seven heads and ten horns, and upon his horns ten crowns, and upon his heads the name of blasphemy.
Revelation 13:3 And I saw
one of his heads as it were wounded to death; and his deadly wound was healed : and all the world wondered after the beast
Revelation 13:11 And I beheld
another beast coming up out of the earth and he had two horns like a lamb, and he spake as a dragon.
Revelation 13:12
And he exerciseth all the power of the first beast before him, and causeth the earth and them which dwell therein to worship the first beast, whose deadly wound was healed.
13 And he doeth great wonders, so that he maketh fire come down from heaven on the earth in the sight of men,
14 And deceiveth them that dwell on the earth by the means of those miracles which he had power to do in the sight of the beast;
saying to them that dwell on the earth, that they should make an image to the beast, which had the wound by a sword, and did live.
15 And
he had power to give life unto the image of the beast, that the image of the beast should both speak, and cause that as many as would not worship the image of the beast should be killed.
16
And he causeth all, both small and great, rich and poor, free and bond,
to receive a mark in their right hand, or in their foreheads
Regardless what these events look like when they are being fulfilled, until they are being fulfilled there couldn't possibly already be an image and a mark in the meantime. Verse 16 says he causes all to receive a mark in their right hand, or in their foreheads. Who causes all? The 2nd beast, the false prophet. The same one in verse 12 that causes the earth and them which dwell therein to worship the first beast, whose deadly wound was healed. Can't do that unless a 7 headed beast has risen from the pit first, and that one of it's heads has a deadly wound that was healed.