Original Lyman (Ideal) sizer dies had a diameter reduction in the form of a hard "step" about .1" inside the mouth of the dies. It shaved away excess metal to attain the finished size and tended to make bullets slightly out of ballance. That stepped design was eventually changed to a taper but I don't know when.
I bought my first Lyman sizer, a #45, about '65 and it came with the new style dies. They gently swage oversized bullets to the final diameter. It seems very unlikely that an even newer #450 would have old style dies, at least as part of the original purchase. Of course, sizers don't come equiped with dies, we have to buy them seperatly. If some dealer still has/had old style dies in stock it is quite possible those would be quietly fostered off on an unsuspecting buyer.
JB has a good idea to soften the older die's steps into a tapered style by honing them a bit but it will require honing inside the sizer just a little bit to reach that stepped part. You will be able to see the step and know when it has been reduced to a taper. Since bullets go far below the top of the die I don't think you would harm anything even if your taper reaming work is somewhat less than perfect.
The only purpose of the "O" ring is to seal the pressurized bullet lube in better, it has no impact on the die's primary function. If I remember correctly, I've read that the insides were modified at or near the same time the "O" ring seals were added so checking inside those without a ring would be wise.
