It might well be. I suspect you know more about them than me.

I've been told, though, that tanks sold to collectors have the barrel(s) filled with cement.

If you download those pics and magnify them, you'll see that even the machine gun barrel in the hull of the tank at left is covered with a mothballing material, perhaps "protectapeel".

That seems rather odd if the barrels are plugged with cement already, doesn't it?

Regarding the possible antique status of a tank--doesn't really matter how old they are, if the bores not cemented, does it? Decommissioned tanks that are officially off the books but never were deactivated would be perfect to quietly pre-position in case of enemy attack or TEOTWAWKI.