In my case, I'd have to define "dead on".
My definition of point blank zeroing is setting up the rifle, sights, and load so that using the same sight picture and point of aim (or aiming point) will put a bullet either into a deer-sized animal or a human sized threat at 100 yards on out to 200 yards.
Dead on, to me, means putting the bullet exactly to point of aim (i.e. aiming at the exact spot you want to hit & having the bullet land exactly there). I don't do "dead on".
This may sound confusing.
Most of my flatter-shooting rifles from .223 on up to .30-06 (excluding the rainbows like the .45-70) are zeroed to strike two inches above my aiming point at 100 yards as a known standard, since that's a more commonly used distance where I'd be more likely to take a shot.
I can use the same sight picture & point of aim (aiming spot on the target) at 200 yards as I do at 100 yards, without holding over or guesstimating & adjusting point of aim, with the expectation of striking close enough inside those two target sizes to be effective, but not with the expectation of striking exactly on the spot I'm aiming at.
In other words, if I were to aim pretty much dead center elevationwise behind the shoulder of a good-sized deer at 100 yards, I'd be no more than two inches above the spot I was actually aiming at & still drop the deer. Aiming at exactly the same spot on the same-sized deer at 200 yards will not put the bullet in either the same exact spot as it did at 100 yards, or exactly at the spot I'm aiming at.
The bullet will obviously drop farther at 200 yards than it did at 100, but if I have a decently flat-shooting caliber & bullet, bullet drop will (if I do my part) be minor enough to still strike the vital area in the torso behind the shoulder and drop the deer.
I can use the same aiming point at 100 and 200 yards with no holdover or guesswork, and the bullet should strike close enough to the aiming point at 200 to be effective.
So, I don't consider a two-inch-high 100-yard zero to put me "dead on" at 200 relative to the bullet striking right where the sights are pointing, just "on" enough to put the front sight in the same place on a reasonably sized target anywhere from 75 yards out to at least 200 and hit the target.
Using a 12-inch plate as a visual aid, if I have my rifle zeroed for two inches above point of aim at 100 yards, the bullet should strike two inches above center if I aim dead center. I won't hit where I'm aiming, but I'll break the plate.
Aiming dead center at 200 yards, the bullet may drop 2-4 inches (depending on caliber & load) and strike two or three inches below dead center. I don't hit the precise spot I was aiming at, but I still break the plate.
This obviously varies with gun & load, but illustrates the point.
A flatter shooting caliber with less bullet drop out to 300 yards is more important in varmint hunting, but not so much in most big game hunting applications. 300-yard shots are outside the norm. If you want to take your rifle out that far, you'll need to shoot it at 100, 200, and 300 yards & learn how much bullet drop you get beyond your basic 100-yard zero.
Some people do zero three inches high at 100, depends on what they know their gun can do & what they want it do do.
Matter of individual choice & requirements.
This point blank range is not limited to 200 yards, by the way, I just use 200 as an example.
Some calibers shoot flat enough to maintain a point blank zero substantially farther out.
Rifles like the .45-70, on the other hand, can require a lot of holdover beyond 150 yards.
Again- the ONLY way to tell for sure what your gun & load will do at 100, 200, and beyond is to shoot it at those distances. Everything else is by guess & by golly.
Denis