«أو لإفادة أن المتكلم عالم به، نحو: أنت حضرت أمس»
Or the report may show that the speaker knows the stated fact, as in: “You attended yesterday.”
If the listener already knows that they attended, “أَنْتَ حَضَرْتَ أَمْسِ” cannot primarily be telling them what they themselves did. It informs the listener that the speaker too is aware of the event.
This is lāzim al-fāʾidah, the concomitant benefit of a report. Reporting a fact ordinarily also shows the speaker's knowledge of it, and in this context that secondary implication is what the speaker intends to communicate.