a curious AT-3400D/AT-3104 (CIS-12) modem configuration

Interesting catch of an AT-3400D modem (also known as CIS-12 or MS-5) running on 14344.0 KHz/USB with the quite uncommon 9 channel configuration (3-out-of-12) as shown in Figure 1 below

Fig. 1

CIS-12, as you know, is a pseudo OFDM 12-tone (+ 1 pilot) waveform using PSK2 or PSK4 modulation at speed of 120 Baud while the modem name is AT-3004D (or its newer counterpart AT-3104). Channels 1-10 are used for data, 11 and 12 are test/service channels, therefore the "aggregate" speed is 1200 Baud. 

Fig. 2

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