Consider how the same information becomes clearer as it is stated with increasing precision and emphasis.
“The students are present”: presence is apparently understood.
“The announcement was made to establish their presence”: the communicative purpose is now identified.
“Every single student is present, all together”: the speaker adds clarification concerning completeness and simultaneity.
These comparisons help explain the grades but do not make every ordinary statement automatically muhkam. The technical criterion of immunity from abrogation is distinct and much stronger.