Consider the limit as more of a guideline. In challenging conditions the examiner will give you extra leeway. The important thing is to recognise that you're left/high/fast etc and correct. Aim for perfection and miss.
The question didn't ask for the limits to be applied by an examiner during a skill test. There isn't a limit set by regulation for an ADF/NDB approach. The indication will of course vary +/- with drift/heading which may change erratically throughout the approach. The ADF can be grossly affected by night effect, coastal effect and electrical storms. In the past with a lot of powerful NDBs then interference from other NDBs could also be a problem. Less so today in the UK as the beacons are turned down in power to tight limits. This can make accuracy very poor as the indicator is motor driven. The most important standards therefore are the height/altitude minimums. To bust those is a no no.