You get the cable box for the new system BEFORE they switch the old system off, or else you wouldn't have service until you got a new box. That's why you saw behavior change with the new box.
It simply isn't possible to send all the channels to customers at all times. There isn't enough bandwidth. So, the cable box at your house negotiates with the central or regional system so only a subset of channels are sent to you. There is no other way to do it in digital cable systems, and the switch to digital was made because it uses significantly less bandwidth than analog.
You get the cable box for the new system BEFORE they switch the old system off, or else you wouldn't have service until you got a new box. That's why you saw behavior change with the new box.
It simply isn't possible to send all the channels to customers at all times. There isn't enough bandwidth. So, the cable box at your house negotiates with the central or regional system so only a subset of channels are sent to you. There is no other way to do it in digital cable systems, and the switch to digital was made because it uses significantly less bandwidth than analog.