i believe there is a 10% tolerance but theres plenty of other things that influence the reading (meter and temp being the most prominent) since they both read low id guess your meter reads a little low. no biggie, i have one of those too.
in general having fewer turns will give a slightly brighter tone with a little less density but tighter bottom
On other forums, people will send pickups back being .1 off of the stated specs (it is revealed that they know little about pickups, and don't care to learn- they know what they know, dammit!).