As long as you are having your scales calibrated annually or twice/year depending on volume, and you've got a margin of error (yes, even calibrated scales have a margin of error) then I really don't see the need for "calibrated" weights.
So you are testing down to 2 kg; let's assume that your package of 2 kg product really has a fill range of 1.90 to 2.10 kg, it probably makes just as much sense to use non-calibrated weights to verify that the scales are "within range" YOU ARE NOT CALIBRATING THE SCALE
I would also not suggest that you leave calibrated weights out and about for daily verification.............at best the calibrated weights (the ones with the certificate) should only be used by QA and only once a week at the most, so you're still going to need weights for daily checks
I think this is the difference between validation and verification