You picked up a pair of gloves that are labeled as 16oz and you get curious to see if they actually weigh 16oz, so you pull out your trusty scale weigh your gloves and you find out that one glove is heavier than the other, maybe you discover that they are lighter than indicated, or heavier than the labeled weight. Throughout my experience I've noticed some brands are spot on when it comes to labeled weight and actual weight, while others aren't. Some brands being grossly over and some within a respectable range of .5 oz-1.5 oz.
I've noticed more and more people becoming increasingly picky about labeled weight and actual weight matching up, but does it even matter? When it comes to fight gloves YES labeled weight and actual weight should be spot on; however, for training gloves I feel it's less important if they are within .5oz-1.5oz range. Ideally you want your labeled weight and actual weight to match; however, this isn't always the case.
So when is glove weight an issue? In my opinion Glove weight is an issue if you notice the difference while training. Let's say you have a 12oz pair of gloves and they feel abnormally heavy. You weight them and find out they're actually 18oz! that is a big issue, since the weight discrepancy is so vast. Another problem would be if one glove is unequivocally heavier than the other causing an imbalance. Most people aren't going to notice acute disparities in ounces and as long as they're in the previously mentioned range it shouldn't be too big of an issue; nevertheless, it all boils down to you and your preference.