[BigJJ]

Agree regarding up to about 3 ounces of weight loss due to water loss.

Weight loss also may result from a break that is repaired and that shortens the bat.

Weight loss will also occur from missing wood - chips, a lot of scoring, carvings, etc.

I am unaware of any evidence that bats may gain weight over time. other than perhaps from a good number of batboy nails or a good amount of tape. I think that is it regarding gaining weight.

But bats recorded as a certain weight, and even bats stamped a certain weight, were sometimes off by a little, from the start. This may be why a bat recorded and/or marked as a certain weight, may actually weigh more. Not due to any weight gain over time, but because the bat began life heavier.