Places that rebuild injectors say that, among other things they:

in order to verify the spray pattern, they fire a laser through the
stream to verify that it makes small particles of liquid in the right
shape

run them at full duty cycle and part duty cycle, firing into a measuring
device to verify that they flow exactly the correct volume of fuel

if you give them 2 or more injectors, they try to make sure that all
the injectors you give them deliver *exactly* the same quantity of
fuel given identical fuel pressure and injector pulse widths.

I wouldn't be surprised if, given normal manufacturing tolerances,
there was a variance of 2-3% on modern, new injectors and 5% or more
on the ancient bosch injectors (when new), let alone once they get
kinda worn.
chris