I think the "only" doesn't mean "only system" but "only if". Because there is a sentence about the case when the system doesn't call. ("The system doesn’t call this method if the synthesizer is in a delay between utterances when speech stops, and it doesn’t call it for unspoken utterances.")

I don't think the "only" means "The system only" but "only if". Because it explains the case when the system doesn't call the methods as well. "(...)The system doesn’t call this method if the synthesizer is in a delay between utterances when speech stops, and it doesn’t call it for unspoken utterances."

I don't think the "only" means "The system only" but "only if". Because it explains the case when the system doesn't call the methods as well. "(...)The system doesn’t call this method if the synthesizer is in a delay between utterances when speech stops, and it doesn’t call it for unspoken utterances."