Basic accuracy (uncertainty) is worst-case for every production model.
If you want to know the best uncertainty, then you have to do some work or have a cal lab do some work for you.
Uncertainty is comprised of an offset and noise. You can, in many cases, characterize the offset and noise and then take steps to try to reduce uncertainty.
Offset is relatively easy to eliminate once you know what the offset is.
As a first step, try to characterize the offset for 100% of range, 50% of range and for zero.
The offset at zero is the easiest to characterize for voltage measure and for current measure.
For voltage measure, short the input and record the reading.
For current measure, open the input and record the reading.
Some DMMs have a REL function. You can use the REL function to eliminate the offset after you measure it.