A320 and safety valve operation
 

has anyone really observed the operation of safety valve in-flight?

In a hypothetical situation, if A320 climbs to say FL410, CPC would maintain cabin altitude max 8000ft, delta pressure would probably cross 8 psi and safety valve may open up at some higher value of delta pressure. ECAM would trigger only if safety valve remains open for a minute or more..

What could be the possible outside conditions in which delta pressure may exceed the threshold for safety valve to operate?

Cabin Altitude remains at some low level e.g. airfield altitude (due manual control of outflow valve, CPC computer failure or outflow valve failed closed). Aircraft climbs towards cruising FL.