I cannot say for sure, but my first guess is that these were not private letters as we normally assume the post is today. Perhaps they were intended to be circulars, or instructive “pastorals” (I don’t know

).
Apperently they were published, and may have been intended for, or expected to be for circulation in the first place. Obviously by the time of the condemnation everyone had read them.
The question then, is why had they read them.
It is interesting that at this time, the Maronites embraced Monothelitism as well. However while the Sees of Rome and Constantinople were no longer occupied by Monothelites shortly afterward, the Maronites continued with it for a longer period.