Yup, that’s one of the many interesting things that nobody knew about. 2-channel mono would have been great for things like audio books. Too bad this was only possible with prerecorded tapes.
What I find interesting is that the tape formatting is completely independent of the audio formatting: tape bullocks, tape frames, inter-frame gaps, modulation, error correction etc. are the lower level, and from that point of view, the audio is just a 384kbps data stream. The PASC / MP1 packets can be anywhere in the stream. So even though the tape transport system may be capable of switching between record and playback at the edge of every tape frame of 64KB, the PASC packets in that stream are not aligned with the tape frames and the audio decoder will always have to resynchronize at the beginning of a new recording.
Another interesting thing is that the DCC system description describes how PASC is encoded and decoded, including the acoustic model (unless I’m mistaken) whereas the MP1 standard only describes how to decode and leaves the encoding to the implementation.