What is the chief difference between “kullu ṭālibin lam yusajjil” and “laysa kullu ṭālibin qad sajjala”?

Supplementary Practice 16: Observing the Sky, Evidential Scope and Rhetorical Precision

• Both say all recorded
• Both say none recorded
• The first negates each student’s recording; the second denies that all recorded
• Only the tense differs