I doubt if bleed extraction changes the performance of the speed control loop in any significant way. If the engine is rated on LP spool speed (I'm assuming here...), maybe there is a debit applied when bleed is requested (to reduce turbine temp) which decreases rated LP speed - thus giving greater margin to NL:max limit..
Also worth noting that at an LP speed, extraction of bleed (from the HPC) would increase HP speed, so unless the debit idea above is true, it would seem that putting AI on reduces margin to NHmax....