I think the key to a controlled firing in a digital controlled firing is to have each zone(as Neil touched on) controlled by it's own thermocouple. One T/C in the middle can not give the control that 3, each in it's own zone can do.The other factor is to make sure the T/C is in good working shape and change it out as it begins to show problems. Have witness cones in each zone to know what the heat work is doing.
Kiln sitter will age out and sometimes fail to shut off, I've had at lest 3 go out over 20 years on different kilns, causing over firing
Stuff happens manual or digital