Generally it is a bad idea, you need to have proper voltage and amperage, otherwise you will cause damage. It is true that there is tolerance for slight variances, but laptops can vary greatly (for example, some take as low as 14v, others as high as 20v). Even if it is the same plug type, if you plug in the wrong adapter, over time it will do damage. The same goes for amperage. There is a distinct difference between 1.5 and 3.5. You can have an adapter that feeds 18.5v and 1.5 amps and if you plug it into a laptop in place of one that fed 19v 3.5 amps, you will definitely cause damage, even if the voltage is close. Be very careful when selecting alternate power adapters.
With that said, in your particular case, it is very close. 1 volt is not a huge difference, but over a long period of time, the variance in force can potentially cause damage to the motherboard. It is usually healthier to have a bit more than a bit less.