Maybe you both are right. Maybe the mold went bad and Diamond changed it out. I've never been in Diamond's factory, but I know exactly where it is at (guess where I live?), and I know that the humidity _RIGHT_NOW_ could very easily make any mold expand.
I'm not saying this happened, and it's not exactly applicable to steel (assuming they're using cast molds here), but when you poly a butcher block surface of any kind in this part of the country it is not just recommended to keep the bottom surface bare, but literally a requirement as the humidity will warp anything around here... (even pad locks!!! Always have bolt cutters in the summer and winter).
BTW, how does a table builder know that the rails are not defective before assembly?
FWIW, I've worked on horrible Diamond tables right there in Louisville, KY not more than 15 miles from the factory, but Diamonds service techs wasn't the ones working on the tables for the last 10 years!!