When there is a matrix it is easier since the camera number is automatically associated to the receiver number, so that when you recall the camera you get control of the receiver with the same number, up to the number of the matrix video inputs.
Without matrix you are just recalling and controlling the telemetry receivers, and the keyboard cannot know how many receivers are connected, so it limits the numbers up to the buttons available on the keyboard (from n.1 up to n.9).
To get control of all the controllable telemetry receivers, actually up to 999, it is necessary to modify a specific parameter in the keyboard menu:
ACCEPTED VALUES -> FUNCTIONS -> RECEIVER CHG -> YES
Afterwards to recall the receiver number you want to control you have to press the button RECEIVER (on the left), then the number (up to 999), then ENTER (on the right).