The source gives situations where Sujud al-Sahw can no longer be performed after the prayer has reached its closing Salaam:
• in Fajr, the sun rises after the Salaam;
• in Asr, the sun reaches its red setting stage;
• after Salaam, the worshipper performs an act that prevents building back onto the prayer, such as deliberate invalidating Hadath or another incompatible act.
A major correction: sunrise here does not mean the completed Fajr itself becomes invalid. The issue is that the pending Sujud al-Sahw drops after Salaam.
The earlier course's invented 'Jumu'ah enters Asr' trigger has been removed because it is not the rule stated in this source passage.