Bent pushrods could be a number of things.
Valves adjusted too tight, pushrod bends.
New built engine has coil bind, bends pushrod.
Valve stuck closed, pushrod bends.
Valve stuck open, valve hits piston and bends valve-bent valve gets shoved into guide and gets stuck harder and bends the pushrod.
Timing chain breaks or cuts loose-valve hits piston, bends valve, sticks valve tighter when bent valve rammed into the valve guide, and bends pushrod.
I think the rule of matching the used valve components is because the parts wear into each other creating different clearances between the parts. Yes, if you place them in various order, odds are that it will work OK, but you will accelerate the initial wear to get them to wear (fit) together again. Also, when dealing with a sphere (like the end of a pushrod) the pushrod sphere wears smaller as time goes on, and the socket gets bigger, creating less surface contact, and a sloppier fit. That in turn creates more lbs. per sq. inches, which in turn promotes faster wear and failure.
