We have A320 CFM and A319/320/321 IAE engined 319 aircraft.
The Flying Manual does not specify limits for the IAE engined aircraft (or I can't see them!) maybe due different FADEC systems?, but on the CFM engined A320's we enter any difference of greater than 1% N1 in the Aircraft Log.
There is no guidance that I can see as to when to abandon, personally I would probably use about -2% as a trigger to set TOGA, and then abort if original planned N1 not achieved.
Having said that I can remember taking off at TOGA from a short runway and seeing a Vib level of 7 units on a CFM engined aircraft, and continuing beyond 80kts with the Vib levels reducing to 3-4 units by V1/Vr and then 1-2 units in cruise. Probably a lot to do with the infrequent need to use TOGA.