I found the reason "It can be decoded at -5 kHz lower tuning below the carrier"
that UZ7HO said. Looking of the reception figure below which received me on
2 Jan 2019, it will be decoded at that moment when the signal began to hear
in Soundmodem. You can see 9k6 spectrum in the FFT of SDR# at the beginning
of the signal. It's the red arrow part in the figure below.
The red vertical line at the center of the 16 kHz width filter is -5 kHz lower
tuning below the carrier. In other words, it was decoding 9k6 in Soundmodem
when I put the red vertical line at 436.9958 MHz in SDR# FFT in the case of
the figure below. It meant that it was "-5 kHz lower tuning".