ive personally found differences that big on one occasion when i for some reason checked my plugs when removed. it kind of threw up a red flag. personally i believe in my case that it was the use of different gapping tools. it ended up i pulled out some dial micrometers and found a roughly 0.01" difference between the two tools i had. they were both the cheap at the checkout round style gapping tools. the one of the obviously lesser quality ended up being the culprit being 0.01" over what it read at 0.035". just a possibility, never know.