Vitas, I see your point about steam and that confirms mine about moisture, look at all the steamed wood we import in this country.
Does open up mean cracks open up on the face? I was always told by my old man that bats fully harden and then are at their best, but they continue to harden and then go past their best and become planks eventually?
That is my definition yes, it generally takes quite a while to get to this point, occasionally a bat will open up early in it's life and this is generally a bat that performs very well indeed. The term opening up is overused and incorrectly used on the forum in my opinion, as explained previously.
As for the other point you made, i think what your old man said is probably true. Modern bats in my view generally get better the more they are used, up until the point where they break. As we know from the knocking in process, the more you hit a bat, the harder the 'crust' on the surface layer becomes via means of compression.
In your Dads case (assuming he is referring to a bygone era of at least ten years ago) i would guess bats back then simply lasted longer as they were naturally air dried and probably carried more moisture. Modern bats are generally kiln dried and i suspect have less moisture content, hence larger sized profiles at similar weights. As a consequence, some longevity can be lost.
So in short, a bat from the past may improve and improve (in simple terms getting harder and harder) over time and at some point will reach its peak and open up. After this point it may start to decline, a modern era bat is likely to break before this point so we never get to the situation where it is 'too hard.'
My opinion/theory of course. I only sell the bloody things, i don't make 'em! I am forever gleaning knowledge though, i will talk to Tony at Hunts about this topic next time i see him.