It could well be that the OP isn't being as gentle and consistent as required to get really accurate trigger weights. Also, it's not uncommon for spring or other scales to be off somewhat.

You might want to get a couple of actual weights, get someone at the local Post Office to verify the weights and use those to practice your technique and check the accuracy of the scale.

Now then, trigger systems tend to polish themselves and become lighter with use. If the weights noted above are accurate, I'd really, and seriously, consider getting them some professional attention. I highly doubt those fall within the range the manufacturers consider safe. I personally wouldn't own a handgun with a trigger that light.