To send a 4 digit account number with the D8112, configure the panel to report in Modem II format.
The only model of D8112 that can transmit modem is the D8112G2. All other models of the D8112 (E, E1, G, G1, A) can only transmit a 3x1 format. These panels allow for a 4 digit account number entry but only three digits are reported .
To properly program the non G2 panels, the account number has to be programmed with a leading 0, or the panel will drop the first digit of the account number. For example, if the account number is to be 123, then it must be programmed into the panel as 0123. The G2 panel, when sending a 3 digit account number, must also be programmed with a leading zero.