Re: Hmmm...
Op-amps gain characteristics are not well defined - vast gain (hundreds of thousands or more) but not precisely defined and not necessarily linear. But they don't need that to be precisely defined because they are used in feedback mode so that the signal on the negative & positive input pins will always end up being almost exactly the same. This avoids having to rely on their precise characteristics. Instead it's the tolerances of the resistors & capacitors in the circuit that count and that's much easier to control than the internals of an integrated circuit.
Op-amps have high imput impedance and low output drive capability and all circuits are designed to expect this without worrying about the exact values. Slew rates are always way faster than needed for audio signals.
The only well-defined specs that are generarlly important is the min/max supply voltage (and therefore output voltage range) and min/max input over-voltage tolerance.