What is the academically careful reading of “they did not ask about isnād”?

Isnād as Part of Religion: Transmitter Competence, Fitnah, and Connected Transmission

• Not one individual ever asked for a chain before the fitnah
• Chains were legally irrelevant during that period
• Systematic source-checking became more prominent after the fitnah
• Textual criticism disappeared after the fitnah