Maximum current drawn from a small 12V A23 battery?
If you're designing for short pulses at moderate currents, then you're limited by the internal resistance of the battery stack over its lifetime and how much that drops the output voltage. At some point, you won't be able to effectively extract power from the battery. The archived datasheet for the similar Duracell MN21 battery gives a spec for a 0.1 s, 400 ohm load, giving a suggested peak load for this type of battery.

The full Energizer application note and this discussion of destructive testing of alkaline batteries indicate that overloading the batteries is a fairly bad idea.

Basically, if you're operating outside of the datasheet specs, you're not getting much guidance from the manufacturers. You haven't given much context about your application, but suffice to say you should consider alternative batteries.